The proper definition of a "starship" is any ship that is capable of travelling between star systems while carrying at least one living crewmember or passenger. Technically, ships that cannot travel between star systems would be referred to simply as "spaceships"; however, because nearly any class of spaceship can theoretically be fitted with some form of faster-than-light drive to allow it to travel between star systems, in practical usage, all ships operating in space are generally referred to as starships. Ships which cannot carry crew or passengers are usually referred to as "drones".
Although starships vary in size and purpose, they are usually grouped together according to common features found on them.
Ships designed primarily to move something from one system to another. That something can be cargo, passengers, communications, or anything else place into and then taken out of the ship.
Couriers are small, fast transports designed to move small payloads between systems in a minimum amount of time. Courier ships that operate in dangerous areas of space may be armed, but they are not designed for use in combat. Courier ships also usually operate with very small crews, or even a single pilot, while the rest of the ship's functions are automated.
Cargo transports are designed for moving larger payloads, and are usually large, slow and bulky ships. As with all transport-class ships, cargo transports are often armed for defense when operating in dangerous areas of space, but they are not meant for regular combat use. Most of the internal space in a cargo transport is given to the cargo holds, fuel storage and FTL drive systems. The cargo area can usually be adapted to the needs of the payload; e.g., a cargo transport designed for moving live animals will have pressurized, temperature-controlled cargo holds. Cargo transports usually require minimal crew, and some smaller cargo transports only require a pilot.
Passenger transports are much like cargo transports, except instead of cargo holds, most of their internal space is used for passenger cabins. Passenger transports come in a variety of capacities, from small taxi-like ships for small groups to huge starliners with space for thousands of travellers. Some commercially-run passenger transports operate on regular schedules between major destinations, while others are available for charter.
Ships designed primarily for attacking targets, for defending targets against attack, or for supporting other warships.
One of the largest warship classes, a carrier is a starship primarily used to transport smaller ships, such as fighters and dropships, to a field of operation. Carriers are usually armed primarily with defensive weapons, such as anti-fighter and anti-torpedo guns. Most of the offensive punch of the carrier comes from its complement of fighters and support ships rather than large ship-mounted weapons, although most supplement this firepower with at least a few torpedo or missile launchers. The carrier also usually includes all of the facilities necessary to maintain the ships it carries, as well as the crews and support personnel needed to operate them. Carriers are the most logistically complex warships in space, but also have the greatest overall offensive capability.
The largest non-carrier warship class is the battleship, whose primary purpose is delivering massive ship-based weaponry to the field of operation. Battleships are designed to engage three main types of targets: orbital or deep space spacestations, planetary targets, and other capital ships in space. Like carriers, battleships also commonly carry an assortment of anti-fighter and anti-torpedo weapons. While battleships also often carry some fighters and/or dropships, they usually do not have the kind of staff and logistical support that a carrier has, so they are more for "odd job" tasks that the battleship may need to undertake if operating independent of a fleet. The lead ship in a battle fleet is usually a battleship. Extremely large battleships are sometimes called dreadnaughts.
A cruiser is smaller than a battleship, and is the smallest warship whose primary purpose is engaging enemy targets in direct combat. Cruisers never carry a fighter complement. Cruisers are usually used either against minor targets where a battleship is unnecessary, or they are used in concert with capital ships in large fleet engagements. Cruisers are best suited for dealing with other ships of similar or smaller size, such as frigates and corvettes, and usually only have minimal anti-fighter and anti-torpedo weaponry.
A frigate is a support warship, not meant for directly engaging an enemy. Many frigates in a warfleet are maintenance and supply ships used to keep the other ships in the fleet operating at peak efficiency. There are also medical frigates for dealing with casualties beyond what the other fleet ships' sickbays can manage. Frigates sometimes also carry additional ordinance for the fleet, such as specialized anti-station or orbit-to-surface weapons, when additional firepower is needed for a target. Frigates usually carry moderate anti-fighter and anti-torpedo weapons, but rely on the other ship classes to survive an engagement.
A corvette is a warship that is smaller than a frigate, but larger than a fighter, and in many ways combines the roles of both. Like frigates, they usually carry specialized weaponry, such as anti-ship torpedoes or anti-fighter drones. However, they are designed to fly into enemy territory and deliver these weapons at close range, like fighters. Corvettes usually have small crews, and rely on their speed and shielding to carry them into and out of battle intact, with little or no anti-fighter weaponry. Anti-torpedo weaponry is unnecessary on corvettes, since they can usually out-maneuver any incoming torpedoes.
A scout ship is a support ship designed primarily for speed and stealth. Scout ships carry light weaponry if they are armed at all, and instead rely on their ability to escape trouble, or avoid it entirely. Scout ships are normally equipped with powerful and sophisticated sensors as well as an assortment of emitters and launchers both for its own protection and to provide assistance to fleet vessels when needed. During peacetime, scouts are often used as small independent exploration and surveying vessels.
Fighters are small combat ships operated by a single pilot or a pilot and copilot. They are generally very fast and maneuverable, with relatively light armor and shielding compared to other warships. Fighters are deployed either from a planet or satellite, a space station, or from a capital ship like a carrier or battleship. Fighters are often deployed in large numbers to try to overwhelm the defenses of the opposition, and it is generally accepted in military planning that not all fighters will survive an engagement.
Fighters are subclassified by the roles they are designed for in combat.
Superiority fighters are designed to go up against other fighters. They carry relatively light weaponry, and provide a good combination of speed, maneuverability and survivability. Superiority fighters are the most common choice as escorts for other ship classes, but also make good multi-role fighters when resources are limited.
Bombers are fighters designed to deliver heavy ordinance to a target and then return. In fleet combat, they are the fighters that carry anti-ship torpedoes and the like. Their maneuverability suffers when they are carrying heavy payloads, so they are usually well-armored to compensate. A true bomber usually has only light weapons for defense against other fighters.
The heavy fighter is a combination superiority fighter and bomber. They tend to be the most heavily armed fighter class, and have respectable armor and shielding as well. While they are not as good at dogfighting as a superiority fighter, the heavy fighter's fearsome weapons make it a threat to ships many times its size. They are ideal multi-role fighters, and can sometimes fill the same role in combat as a corvette when used against sufficiently inferior enemies.
An interceptor is a fighter designed to be faster than any other combat ship in space. Its main purpose is catching and destroying bombers before they can release their payloads, but they can be used against any small ship. Interceptors are designed more for straight-line speed rather than maneuverability, and aside from their specialized ship-killing ordinance they are lightly armed, so they usually make mediocre dogfighters.
Ships designed specifically to deliver personnel into a combat area are called dropships. The term comes from armed shuttles designed carry Marine squads from a capital ship in orbit to a combat zone on the surface of a planet -- literally, the ship was dropped from the host ship, and allowed to freefall into the atmosphere, trying to reach its destination in the shortest time possible.
In addition to orbit-to-surface dropships, there are also ship-to-ship dropships. These are generally very heavily armored troop shuttles equipped with hull-breaching charges and a universal docking couple. The dropship attaches itself to a ship to be invaded, attaches the docking couple, then blasts a hole through the outer hull to create an entrance for the troops. It is a highly risky insertion method, so the troops are usually equipped with pressurized Powered Armor suits to protect them.
Starship weapons, like starships themselves, come in different classes and types. The following are examples of weapons in use currently, but is not necessarily exhaustive.
Directed energy weapons are weapons whose destructive force comes from an energy or matter stream projected into space without a physical vehicle. The most basic example of a directed energy weapon would be a laser, although lasers are generally considered too weak and too easy to counter, and are very rarely used for actual combat.
Beta Tachyon Beam
A large weapon that can only be carried by larger classes of starship due to its high power requirement. The beta tachyon particles used in this weapon are unusual in that they are mostly unaffected by traditional energy sheilding. They survive for only a short time (meaning the weapon can only be used at relatively short range), and cause molecular and atomic bonds to fall apart on contact, with extremely high penetration. This weapon's extreme destructive potential has caused it to be banned from use by interstellar treaty, although they are occasionally still seen on rogue ships.
Balllistic weapons are weapons that fire a physical projectile into space intended to cause damage when it strikes its target. They differ from self-propelled weapons in that the projectile in a ballistic weapon does not accellerate on its own once it is fired. A basic example of a ballistic weapon would be a machine gun.
Self-propelled weapons are weapons that fire a projectile that accellerates after it has been fired. Self-propelled weapons very often also have a steering and guidance mechanism to allow it to change course in order to intercept its target. A basic example of a self-propelled weapon would be a heat-seeking missile.
Other types of starship weapons exist, but are seen far less often than the above.