Syncopation is where the emphasis is on a note other than the one expected. It could be that there is an irregular pattern in the group perhaps as the result of a brief quaver length pause that should be where the emphasis falls. It could be that the music has been composed in a way that has dotted crotchets paired with quavers. There are many different reasons for creating the imbalance on the beat but usually it is done purposefully and to create a certain effect.