Monopods or unipods use the same basic principles as tripods, but they are only single legged supports. It is basically a single pole which lets you mount a camera on a swivel/tilt head. They are useful for keeping cameras steady for location work and when a tripod may be too awkward or bulky to use.
It isn't a good idea to use a monopod though if you are using large or heavy cameras or if you are going to be using shutter speeds below about 1/15 second. Make sure the monopod can support the weight of your camera. If you stand or kneel with a monopod braced against your body or leg it can give your camera much needed extra support and steadiness, allowing you to take vibration, shake free shots that should be blur free. Monopods are good for sports and for photographing over peoples heads.
Monopods come in various sizes, styles, colors, materials and weights. They range in price from about $20 to a few hundred. Cases are also available.