Shareware is software which you can legally use for a short time without paying for it. Unlike regular commercial software, it is not illegal to copy shareware and give it to a friend. However, the authors of shareware expect that if you like their software and use it regularly, you will send them some money.
Shareware comes with no guarantees, and it is usually less sophisticated than commercial software.
However, many shareware programs are quite powerful and useful. After you have used a shareware program a few times, you should send some money to the author to become a registered user. As a registered user, you will often be sent the latest version of the program, a printed manual, and you may be able to get help in using the program. Shareware is an easy way to distribute software to a large number of people without having to print manuals, create thousands of diskettes, advertise, and work out deals with retailers. You can obtain shareware from a computer store, or you can get it from an on-line data service.