When a wrestler takes a move and acts like it didn't affect them at all. Sometimes it's a deliberate power move — Undertaker sitting up after a finisher, Hulk Hogan 'hulking up.' Sometimes it's a wrestler being unprofessional and refusing to make their opponent look good. Context is everything. A well-timed no-sell is iconic. A petty no-sell is career poison.
"He hit him with three German suplexes and the guy just stood up and stared at him. The no-sell popped the crowd huge."