slow clap

Short definition from Wiktionary

Noun

1. 1
   A form of clapping in which audience members clap slowly, with long intervals between claps, as a form of heckling and to show that they disapprove of a performer, speaker, etc.
2. 2
   A form of applause (especially used in films for dramatic effect) that slowly crescendoes from one person's clapping to a crowd's.