Cover is a very busy section on the off side. The best fielding players are usually positioned on cover since their main role is to prevent the batsmen from scoring runs.
Similar to point, cover has also similar or nearby positions. Extra cover is positioned more in direction of mid-off, down the field.
Short extra cover is similar to extra cover but closer to the pitch, were they can catch the ball out of the air.
Deep extra cover is at the same height as cover, but closer to the boundary. The role of players at deep cover is to prevent the ball from crossing the boundary.