Prime
From Speedsolving.com Wiki
Prime refers to a ' symbol in standard notation, SiGN, and Singmaster notation or, much less frequently, an i. Prime symbols follow initial move letters (F, U, R, B, L, and D on the 3x3x3) to indicate that the layer is turned counterclockwise by one turn. If it follows a letter and a 2, it means the layer is turned twice counterclockwise.
Prime is also synonymous with "inverse", "backward", etc., however, cubers generally use the term "prime" and tend to stay away from other names.
