Cur refers to a dog, usually of mixed ancestry. In common usage, the term is often derogatory; fighting dogs that regress to growling rather than maintain calm are referred to as 'curs'. The derivation of the word "cur" is uncertain. According to the Dictionary of True Etymologies (Room, Adrian, Routledge & Kegan Paul, London and New York, 1986), "cur" is a Germanic word, possibly from Old Norse meaning to growl. If so, then the word is onomatopoeic, and a cur is a dog that goes "grrr."

Cur is also a category of hunting dog developed in the United States, usually not recognized as show dogs but developed solely for their hunting ability. As a result, most of the cur breeds are types rather than breeds—that is, one of these dogs can be recognized as a certain type of Cur but the appearance standard is extremely flexible, enough so that a complete breed appearance standard is difficult to create. However, several kennel clubs register various cur breeds based on their ancestry (bloodlines), and several lines are recognized within each breed. The United Kennel Club has an active registration program and competition hunting program for these dogs.