Shareware is a distribution method, not a type of software.
Shareware distribution gives users a chance to freely try software before they buy it.
If you try a Shareware program and continue using it, you are expected to pay a registration fee. And because the overhead is low, prices are also low. There are real advantages to you in the Shareware system. You get to try out software to make sure it is compatible with your hardware and that it fits your needs before you pay for it. The author saves the expense of advertising, packaging and distribution and passes the savings on to you.