A cricket ball can be made up of two or four pieces.
The inside is made of cork, with two halves of leather then wrapped around the outside as a casing.
The leather is then stitched together to form the "seam".
This is slightly raised, which is why seam bowlers try to get this part of the ball to hit the pitch when it bounces and make the ball move in a different direction.
The leather of the ball is polished, but the fielding side will try to keep the shine on one side and hope that the other half is roughed up.
It's the shine on one side of the ball that can make a ball swing through the air.
A white ball is used in one-day and Twenty20 cricket as it is easier to see under floodlights and against coloured clothing.