Depends on the medium and what field roles exist. For instance:
Boat: any vessel that operates from a parent ship or station and generally does not or cannot stray far from their home.
*Small Boats
Skiffs (think Vasama): minimal everything
Runabouts, Shuttles, & Lighters: small general-utility boats (eg Hedron), sometimes specialized between small cargo or personnel loads
Cargo Lifters/"Lifters": sometimes subdivided between light and heavy models, often capable of reaching nearby stations on their own
*Attack Boats
Interceptor: fast, light, agile, often fragile but at least as well-armed as any fighter
Fighter: one-man attack boat, average armament, armor, and with a decent speed
Gunship/Gunboat: a two-man attack boat, often with a turret and/or troop bay
Assault Boat: an armored gunship with larger troop accomodations and engines and smaller weapons compliment
Brawler: aka Bomber, large weapons allotment and often sports two or more turrets controlled by one crew each, the smallest boat that can require a command position among the crew
Patrol Boat/Heavy Gunboat: typical of the Lancer and Lictor, the bridging line between "boat" and "ship", turrets are often grouped into "batteries" where one crewman controls multiple emplacements
*Private & Commercial Ships
Yacht: effectively a large, very long range pleasure boat with notable crew and passenger accomodations, it is effectively classed as a starfaring ship.
Haulers/Tankers/Starliners/Freighters/Icers/Exoriers: large cargo vessels typically with dedicated loads, namely Icers and Exoriers which are built especially for the transport of propellant or fuel rods, respectively, and Starliners for luxury tourist transport. They can vary in size from the smallest ships to obscenely large much the same as private yachts. Haulers can also be outfitted as large mining, salvage, or repair rigs.
Fleet Supply Ships: essentially any class of hauler that operates under a faction directly to provide logistical support to its combat elements, may or may not possess token defensive armament
*Escorts
Corvettes/Cutters: capable of longer ranges and higher speeds than a patrol boat, though often coming in around a similar size or slightly larger, they aren't made for stand-up fights
Frigate: a support ship in most cases, often specialised for specific roles, built for speed over combat endurance, support carriers are a type of large frigate
Destroyers: where a frigate is separated into combat support roles with specialised equipment, destroyers are often specialised by armament and target preference, typically for anti-boat or missile strike operations, heavy-gun destroyers are also somewhat common in older or less-modern fleets, trades overall speed for firepower and armor
Capital & Sub-Capital Ships: hereby defined under Starbase terminology as any ship made predominantly of larger station pieces to achieve their size within the game engine's limitations.
*Cruisers: a combination of firepower, armor, and specialised support equipment, cruisers can serve in mainline combat and meet their specialised mission objectives.
Assault Carrier: large enough to hold and service a significant compliment of attack boats and one or more shuttles, lighters, or light cargo lifters and support a dedicated boarding action against a small station
Battlecruiser: a heavy-gun cruiser that can "sink anything that can catch it", often with minimal or nonexistant special equipment
*Battleships: the absolute largest a ship that can be made, typically dedicated to a very specific role, most are combat-oriented platforms and represent a significant investment of capital and personnel. The two most iconic battleships are the fleet carrier/supercarrier which can house a massive force of attack boats and is sometime specialised for boarding actions as a "battlebarge" and the all-heavy-gun dreadnought possessing overwhelming firepower and armor thick enough to stop a railgun from penetrating critical sections, the even larger superdreadnought sacrifices speed for even more offensive and defensive capability and is closer to a mobile fortress than a ship. The mobile shipyard can be termed a highly specialised rear-echelon support battleship and often mounts token anti-boat defenses so as to be classified as a "warship" when factions get competitive about comparing fleet sizes.