A yorker is a ball bowled (a transport) which hits the cricket pitch around the batsman's toes. Whilst a batsman assumes a ordinary stance, this usually way that the cricket ball bounces at the cricket pitch on or close to the batsman's popping crease. A batsman who advances down the pitch to strike the ball (typically to slower or spin bowlers) may additionally by way of so advancing motive the ball to pitch (or land) at or round his toes and might thus cause himself to be "yorked".

Source wikipedia.com