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Webster 1913 Edition

Noun.

Action carried on aside, and commonly in dumb show, while the main action proceeds.

See also: by-play

byplay ‎(countable and uncountable, plural byplays)

(theater) Any action, carried out onstage during a performance, apart from the main action.
- 1983, Frank Northen Magill, Magill's American film guide (volume 1, page 647)
  The father-son byplay is occasionally overdone and tedious, but there is a genuine warmth in both the Oland-Luke and the Toler-Sen Yung teamings.

any action carried out onstage during a performance, apart from the main action