Selenium is a test tool for web applications. Selenium tests run directly in browsers like Internet Explorer, Mozilla and Firefox on Windows, Linux and Macintosh. As they say in the very first paragraph on the seleniumHQ website: Selenium automates browsers.
You should also keep in mind that Selenium can do a lot more than testing too, such as taking care of web-based administration tasks that you know you should automate but haven’t yet gotten around to doing.
The site also claim that Selenium is supported by the biggest browser vendors, who will adopt it as a native part of their browsers.
