Imagine facing a leg break. Now imagine the ball hurtling down at you at 80mph.
It's where the ball moves off the pitch from the batsman's leg-side towards the off-side.
The amount of movement will depend on the bowler, state of the pitch and the condition of the ball.
If bowled on or around the batsman's off stump, it will give a bowler a greater chance of getting an edge to the wicketkeeper or slips.
With the seam vertical, the middle finger is placed along the seam with the index finger about two centimetres away.
The ball rests between the thumb and the third finger.
As the ball is released the index and middle finger work down the side of the ball so that the thumb passes round under the ball, generating spin on the ball.