Players positioned on mid-off are close to the bowler. The main role of the player at mid-off is to cut of straight dives.
He has to stay on his toes as the ball comes very fast at this position.
There are some similar or nearby positions. Deep mid-off is behind the mid-off position, used to prevent the ball from going out to far.
Silly mid-off is next to the batsman. The role of players at silly mid-off is to catch bad-pads, bat hits or easy targets.
Long off is directly at the boundary, preventing the ball from crossing it.
Notice, the same position exists on the on side (leg side). It is then called mid-on, silly mid-on and long on.