According to Dictionary.com, "glutes" is a slang abbreviation that refers collectively to the gluteal muscles, especially the gluteus maximus. These muscles make up the buttocks. This abbreviation is most commonly used in the context of exercise.
Many weightlifting exercises are employed to target the gluteal muscles with the intent of making them larger in appearance and stronger. For example, the squat and deadlift work the entire lower body and much of the upper body, but they also have a significant effect on the glutes when performed with good form. Many isolation exercises are also used to develop the glutes, including lever lying hip extensions and barbell hip thrusts. The glutes are also employed extensively during running and sprinting.