Gus is a masculine name, often a diminutive for Angus, August, Augustine, or Augustus, and other names (e.g. Aengus, Argus, Fergus, Ghassan, Gustav, Gustave, Gustavo).
As a stand alone masculine name, it derives from the Old Irish word gusmhar or gusair for "strength" or "force" or the root gustu- for "choice"/"chose", with most naming books combining both derivations as "strong choice".