In Current Use:
Cruisers can refer to a number of ship types across human space. Descended from the Age of Sail term, a Cruiser refers to a ship capable of long distance/long duration missions. Common subtypes of cruisers include the frigates and corvettes.
While different names are used in different navies, a Lineship is a large capital ship, intended to operate in a line of battle. Intended to fight other large capital ships, Lineships carry heavy broadsides and typically rely on smaller ships for for support against smaller ships.
Sloops are small spacecraft, analogous to fighters otl, incapable of operating independently of a supporting vessel. While many cruisers and lineships carry small formations of sloops, most navies also field dedicated sloop carriers. Often the largest combat unit fielded by a navy, a sloop carrier typically has extremely limited offensive weaponry, instead using it's complement of sloops to launch strikes at extreme range and relying on smaller vessels to keep enemy vessels away.