Humans spontaneously synchronize to a broad range of stimuli: synchronized walking, turn-taking in conversation, marching, dancing, and the in-unison singing of "Happy Birthday." Synchronization is shown especially in dance, where planned coordination is the goal. Dancers' sophisticated timing skills are particularly important for coordinating with other dancers in duet or group choreography/improvisation. The term entrainment is usually paired with the notion of coordinated rhythmic movement. It describes a phenomenon in which two or more independent rhythmic processes synchronize with each other.