An exercise you would do in a gym. Basically consits of two parallel bars raised to some height. You are to stand between the bars and raise/lower yourself using only your hands. It works your triceps and latissimus dorsi as well as a bit of your shoulders.

Note that sometimes there are assisted dips. Basically there's a counter weighted leg rest which allows you to control how much weight you're going to be lifting. If you want to work on your tricepts I suggest this.

There are a couple of drawbacks:

1. Your wrists WILL hurt if not done properly (and quite possible even if done properly)
2. Your shoulders will also hurt the first few times you do it

Just like with everything you do, consult your doctor if you're unsure or experiencing weird pain. Good luck.

A biomechanical word of caution: When doing dips it is tempting to exaggerate the range of motion, stretching the pectoral muscles and anterior deltoids. Avoid this at all costs unless your shoulders are made of titanium.

Although a full range of motion is desireable for most exercises, it can be overdone. Do not allow your elbows to clilmb past the plane of your shoulders. Bottoming out dips will nearly guarantee tendonitis or a rotator cup injury.

I know this because after two weeks of weighted dips, going as deep as possible, raising my right arm to do anything other than drink coffee was impossible.

Dips are actually safer and more beneficial than bench presses for gaining upper body size and strength so by all means do them. Just be smart about it.