To delay or avoid showing one's hand at showdown, forcing other players to expose their hands first. When done while holding a good hand likely to be the winner, it is considered poor etiquette, because it often gives other players "false hope" that their hands might win before the slow-roller's is exposed.
SLOW ROLL
Meaning of SLOW ROLL in English
Poker English dictionary. Английский словарь покера. 2012