Class IV is a starship classification term used to describe a type of starship in relation to other starship types in similar fleets.
In the 23rd century, the Orion Colonies' Lightning-class starship was considered to be a class IV blockade runner by the Federation Starfleet. (FASA RPG module: The Orions: Book of Common Knowledge)
In the 24th century, the Achilles-class starship was considered to be a class IV warship by Starfleet. (DS9 video game: Dominion Wars)