Turn construction unit
A turn construction unit (TCU) is the fundamental segment of speech in a conversation, as analyzed in conversation analysis.
The idea was introduced in (Sacks, Schegloff, & Jefferson 1974) and is meant to describe pieces of conversation which may comprise an entire turn. The end of a TCU, called a transition relevance place (TRP), marks a point where the turn may go to another speaker, or the present speaker may continue with another TCU.
References
Sacks H, Schegloff E A, Jefferson G. "A simplest systematics for the organization of turn-taking for conversation." Language 50 (1974) pp. 696–735