Selenium automates browsers. That's it. What you do with that
power is entirely up to you. Primarily it is for automating web
applications for testing purposes, but is certainly not limited to just
that. Boring web-based administration tasks can (and should!) also be
automated as well.
Selenium has the support of some of the largest browser vendors who
have taken (or are taking) steps to make Selenium a native part of
their browser. It is also the core technology in countless other browser
automation tools, APIs and frameworks.