The deliberate shifting of the accent to a weak beat or an off beat is called syncopation.
Strong beats are naturally accented beats, in 4/4 beats beat 1 and beat 3 are strong beats and beat 2 and beat 4 are weak beats. Syncopation is used in many music styles. The types of syncopation are: suspension,even-note syncopation, off-beat syncopation and anticipated bass.