The most common type of webbing for outdoor sports is 1 inch tubular nylon webbing. Webbing is used for slings, runners, harnesses, anchor extensions, and quickdraws. Webbing usually comes on a spool and is sold by the foot. Many colors are available. The color doesn't mean anything, so pick your favorite. Webbing often has at least one tracer (a colored thread that runs the length of the webbing). I've heard people say that the number of tracers in the webbing is an indication of the strength, but I'm pretty sure this is just an urban legend. It's a good idea to carry at least 50' of webbing with you on canyoneering or caving trips and at least 15' of webbing when rock climbing.
Webbing is generally cheaper than rope.
Webbing is harder to tie than rope, and many knots that work on rope do not work on webbing.