Selenium is a free (open source) automated testing suite for web applications across different browsers and platforms. It is quite similar to HP Quick Test Pro (QTP) only that Selenium focuses on automating web-based applications.
It came from a joke which Jason cracked one time to his team. Another automated testing framework was popular during Selenium’s development, and it was by the company called Mercury Interactive (yes, the company who originally made QTP before it was acquired by HP). Since Selenium is a well-known antidote for Mercury poisoning, Jason suggested that name. His teammates took it, and so that is how we got to call this framework up to the present.
Selenium is not just a single tool but a suite of softwares, each catering to different testing needs of an organization. It has four components.