As galactic civilization evolved and interaction between different species and their states became commonplace, standardized terms evolved to classify spaceships according to their size and the role they fulfill.
A freighter is any vessel designed primarily for the transport of goods. They come in varying shapes and sizes, making it difficult to classify them furthern than that. Specialized freighters exist, catering to any needs a specific type of carge may impose upon the transporter: ventilation, temperature control, life support, to name but a few.
Cruise Liners are civilian traffic vessels for longer distances, providing accomodation for the daylong travels between different planets. They provide a myriad of services and especially those that service longer routes spanning several systems tend to feature amenities as found in a small city. They are also operated for joyrides, flying trips to particularily scenic destinations.
Usually the smallest civilian vessel found, a Yacht is a private civilian vessel accomodating no more than a handful of individuals at once while providing all systems for longer interplanetary flights. They are usually a status symbol for the particularily wealthy or powerful.
Both fighters and bombers are minor vessels without sophisticated life-support and only limited fuel reserves, generally not powered by reactors or similiar power-solutions. They are generally used in different auxilliary roles in ship-to-ship combat.
Bombers are generally thought of and used as autonomous missile platforms capabable of coping with advanced electronical counter-measures as well as electromagnetic pulse defenses due to the presence of a human pilot.
Fighters are primarily used to intercept the threat posed by both bombers as well as missiles and are used as defensive assets for major ships as well as entire fleets.
Additional designations to both fighters and bombers include a scale ranging from light over medium to heavy, describing the relation between armor and acceleration speed of the vessel, as well as its tactical rule. In general, light units are supposed to evade enemy defenses, while heavy units are designed to operate in the dense crossfire between major ships in battle.
Sometimes, the designations ultra-light and super-heavy are used to describe vessels that go beyond in their commitment to either acceleration or armor. Ultra-light fighters, however, may often also be referred to as scouts and serve a distinctively different role in combat: that of independent sensor platforms in advance or far flank of a fleet.
Gunboats are the smallest vessels capable of independent interstellar operations and often feature no more than a single individual as crew, limiting their de facto operational distance and time. While possessing sophisticated life-support and larger energy-sources, they are generally dependant upon spacebases or at least larger vessels to refuel, resupply and maintain the ship. As a consequence, gunboats are most popular for policing duties as well as orbital defense missions.
Corvettes are small combat ship designed primarily for fleet defense and escort missions and thus feature a heavy focus on point-defense weapons. The necessity to keep up with civilian shipping limits the amount of armor found on these types of ships, who instead often possess comparatively powerful reactors and engines, increasing acceleration speed of corvettes.
Usually only slightly bigger than corvettes, fregates tend to employ more versatile weapons and while common as fleet support, may just as likely be encountered in independent operations. Fregates differ from their cousins, the corvettes, in that they are geared towards actual ship-to-ship combat, usually possessing at least one major anti-ship gun as well as ship-to-ship missiles, instead of the sophisticated point-defense assets of a corvette.
Ever since the groundbreaking design of the Nova-class Fregate, fregates often feature docking bays for one to three fighters or bombers.
Destroyers are medium sized, heavily armored ships occupying a defense and escort role similiar to the corvette, but on grander scale. Like the corvette, though considerably larger in size and bulk, destroyers are mainly armed with point-defense weapons and small calibre guns. However, destroyers are designed to operate as protection of major combat vessels, like cruisers and battleships, and not so much as escorts for civilian vessels. This is reflected in their heavy armor as well as their capability to lay dense fire on enemy vessels in order to overwhelm enemy targeting and defense systems.
Cruisers are the smallest of the capital ships, designed as flagships for minor fleets or for independent operations. Armor and weapons are designed to make the ship versatile and adaptable to different situations. These ships also usually feature major weapons for spacecombat that can potentially penetrate even the armor of battleships.
As large as a battleship, battlecruisers are amongst the largest ships to be encountered in space combat. Their firepower is unsurpassed, on par with that of their siblings the battleships. The only distinguishing feature between these two ship classes is that a battlecruiser possesses lighter armor, allowing for higher acceleration and cheaper construction costs. This in turn means that battlecruisers are usually used for flanking and long range fire and do not engage enemy fleets head on.
Battleships are the most powerful vessels in space, unsurpassed in terms of size, armor and armarment. They can survive sustained fire while dealing severe punishment themselves. These ships are almost exclusively used as heart and center of major fleets, delegating any other class of ships present to mere support roles for the main combat asset that is a battleship. Battleships are also used, due to their thick armor, to break blockades, for example at interstellar gates.
Carriers are mobile platforms for fighters and bombers to be used in a fleet support role. They come in various sizes and are usually classified into light, medium or large carriers, depending on the number of squadrons of fighters or bombers they carry. In combat, carriers tend to evade enemy engagements, instead deploying their squadrons to flank hostiles, distract them or protect the flanks of their own fleet. To this end, carriers tend to have high acceleration and little armarment beyond strong point defenses intended to keep enemy bombers at bay.