An adjacency pair is a unit of conversation that contains an exchange of one turn each by two speakers. The turns are functionally related to each other in such a fashion that the first turn requires a certain type or range of types of second turn.
(English)
Levinson, Stephen C. 1983.Pragmatics. Cambridge, England: Cambridge University.
Crystal, David. 1987.The Cambridge encyclopedia of language. Cambridge, England: Cambridge University.