Gar can refer to different things, depending on the context:

1. Fish: Gar is a type of fish that belongs to the family Lepisosteidae, which are the only surviving members of the Ginglymodi, an ancient holosteian group of ray-finned fish that first appeared during the Triassic, over 240 million years ago. Gars comprise seven living species of fish in two genera that inhabit fresh, brackish, and occasionally marine waters of eastern North America, Central America, and Cuba in the Caribbean. They are slow-moving fish that prefer the shallow and weedy areas of rivers, lakes, and bayous, often congregating in small groups. They are voracious predators, catching their prey in their needle-like teeth with a sideways strike of the head. They feed extensively on smaller fish and invertebrates such as crabs. The largest member of the gar family, the alligator gar (Atractosteus spatula), can measure up to 10 feet long and weigh over 300 pounds.

2. Grand Army of the Republic (GAR): The GAR was a fraternal organization composed of veterans of the Union Army, Union Navy, and the Marines who served in the American Civil War. It was founded in 1866 in Decatur, Illinois, and grew to include hundreds of "posts" (local community units) across the North and West. The GAR initially grew and prospered as a de facto political arm of the Republican Party during the heated political contests of the Reconstruction Era. The commemoration of Union Army and Navy veterans, black and white, immediately became entwined with partisan politics. The GAR promoted voting rights for Black veterans, as many white veterans recognized their demonstrated patriotism and sacrifices, providing one of the first racially integrated social/fraternal organizations in America. The GAR was organized into "Departments" at the state level and "Posts" at the community level, and military-style uniforms were worn by its members. There were posts in every state in the U.S., and several posts overseas. The GAR was dissolved in 1956 at the death of its last member, Albert Woolson.

3. Interjection: Gar can also be used as an interjection, meaning "by gar," which is a mild oath.