Someone who participates in a beta test. Most often, they use a piece of software until their eyes bleed. Then they write really tedious reports on what kind of bugs, glitches, and other weirdnesses they encountered. Beta Testers nearly always get software before anyone can. Though, most times, the coolness factor of having something brand spanking new, is overrided by the fact that it actually requires work.

A beta tester is also somebody who likes to have the latest version of ay kind of software (or hardware for that matter). You sign up with the manufacturer and get to use it before most others. In the good old days to be a beta tester used to mean that you got paid for your effort, or at least got to use the product for free. When I say "paid" I don't necessarily mean in hard cash. Most of the time it meant that you got a full product for free once it shipped. Nowadays this doesn't happen for different reasons.

• Software never leaves beta stage. That is specially true for shareware and freeware. Kind of the same symptom as the "under construction" sign on web sites. Everybody knows that software is never perfect nor finished, but by leaving the beta name in there you make sure that nobody get's really annoyed if it suddenly doesn't work.
• Companies like Microsoft have realized that a lot of people really want to get their hands on the product early, that they are actually prepared to pay money for the privilige of using unfinished software.
• It can also be a way of making some of your customers feel special by letting them "take part" in the development work and come with "useful input" on the product and its development traject.