Source:
http://tennis.about.com/library/blswingweight.htm
Definition:
Swing weight describes how heavy a racquet feels when it is swung.
Swing weight increases as the racquet's weight is distributed more toward the head, so head-heavy and extra-long racquets have a high swing weight in relation to their stationary weight.
A higher swing weight results in low maneuverability, but generally more power output.
Source:
http://www.sportscomet.com/Tennis/219515.htm
Swing weight is the measure of how heavy a racquet feels when you swing it.
There are 2 major things and 1 minor thing to take into consideration when talking about swing weight.
The majors are (A) the actual racquet's weight, and (B) the racquet's balance.
The minor is the racquet's length.
The rule of the thumb is heavier racquets have a higher swing weight or in other words there is more weight that you're transferring through the racquet and into the ball when you swing.
Generally head-heavy racquets have a higher swing weight than head light racquets, but my suggestion is lean towards head light. The head light do less injury prone to your body and if you don't like how it feels, you may opt to use lead tape.
The longer a racquet the more weight behind it, and vice versa, the shorter a racquet the less weight behind it.
Focusing more on the racquet's weight and balance. The harder you hit the ball, a heavier racquet will be more solid and stable. While, a lighter racquet will give you more head speed if you have a slower swing.
Note that a heavier racket requires more energy to get the head around the ball, while a lighter racket will need less energy.
Source:
http://shuttle-house.com/new-cgi/ite...GOSEN&hid=GM31
Badminton Swing Weight Measurement Machine