back channel response

n. Any short utterance such as uh-huh, yeah, or right produced while the other person in a conversation is speaking which indicates attentiveness, does not interrupt the other person, and does not require acknowledgment by the other person. These typically account for one-fifth or more of all utterances in American English and differ greatly among languages and cultures. Linguistically or culturally inappropriate back channel responses or a lack of such responses contributes significantly to difficulties in crosscultural communication.