Over the Top
This swing characteristic is very common in higher handicap golfers. This commonly occurs with overuse of the upper body on the downswing portion of the swing. The player brings their club from outside to in and does not keep in in the slot. The slot is the intended swing path of the club that is ideal to put the club face squarely on the ball.
Shot Implications
If you have this swing characteristic it is common for you to pull the shot if your club-face is square and for you to slice the shot if your club face is open at impact. This fault makes it very difficult for you to consistently strike the center of the club face when you make contact with the ball.
Body Limitations
This swing characteristic can be seen if you have a hard time with disassociation. Disassociation is huge in the golf swing; this is the ability for you to keep one area of your body stable while moving another part of your body. Their is an ideal sequence to moving the parts of your body during the downswing. If for instance you have stiffness in your hips or pelvis and they are not moving effectively, it is not uncommon to see a golfer using more of their upper body to swing the club, this often leads to the over the top swing fault.
A proper weight shift is also critical to prevent this swing fault. A right handed golfer shifts their weight from the trail leg the lead leg very early in the downswing. If you have poor balance, or decreased core and glute strength it will force you to not shift as effectively and you end up coming over the top.
Exercises/Corrections
There are drills you can perform to help with disassociation, and mobility of the upper and lower body.
The Brettzel : http://www.mytpi.com/improve-my-game/swing-characteristics/over-the-top_v2
The stretch above is a great way to work on your mobility and the stretching of key areas in your body that need mobility to make a powerful golf swing.