The classic overlap comes from a full-back running past a winger who has cut inside. It creates a 2v1 against the opposing full-back and often ends in a cross or a cut-back.
Modern variants include the underlap (the full-back runs inside the winger) and the inverted-full-back reversal, where the winger overlaps a player who has tucked into midfield.
Overlapping runs only work if the ball carrier holds the ball long enough to bait a defender into committing, and the runner times the sprint so the pass lands in stride.