Gar is a short form of the given names Garfield, Garnett, or Garrett. It's of English origin and means 'spear strong'. The name was popularized by characters from literature and media, such as the comic strip character Garfield the cat. Gar can also be used as a shortened version of other names starting with 'Gar', like Garret, Garvin, or Garnier.
"Gar was quite popular from the late 1940s to mid-1960s, peaking with 16 births in 1958. After that, it declined significantly."