Cross-rhythm is the effect of two notes being played against three (e.g. in piano music it might be groups of two eighth-notes (quavers) in the right hand and groups of triplets in the left hand).

Cross-rhythm is is also the effect that occurs when the accents in a piece of music are different from those suggested by the time signature (e.g. the division of 4/4 time into 3+3+2 eighth-notes).