Space animal is a collective slang term within the Smash community that commonly refers to the Star Fox characters (Fox, Falco, and Wolf). The terminology arose out of the study of competitive Super Smash Bros. Melee, where in the stark similarity between Fox and Falco's physical properties (most importantly high falling speed, high gravity, and light weight) can be exploited by other characters in similar ways, such as in chain throws from characters such as Marth up throw chain in Melee and Pikachu's zero-death down throw chain throw in Brawl or specialized combos such as Melee Jigglypuff's space animal slayer. With the release of Super Smash Bros. Brawl, Wolf became lumped into the group, being vulnerable to many of the things they are, despite his higher weight.
Many of the fundamental similarities between Fox and Falco in Melee are shared by Captain Falcon, as well as in Brawl; as a result, Captain Falcon is vulnerable to many of the combos and chain throws that afflict them despite his much heavier weight, and is sometimes considered part of the space animals in some circles despite not being a Star Fox character.