How it got this name Selenium-
Once jason cracked a joke within his team it was regarding the another automated testing framework (QTP) that was popular during Selenium's development, and QTP was made by the company called Mercury Interactive, Since Selenium is a well-known antidote for Mercury poisoning, Jason given that name and his team members took it.
Currently It has four components -
first Single Selenium rc came into light and is named as Selenium1 later in 2008 when Selenium Team decided to merge Web Driver and Selenium RC to form a more powerful tool and merging of Selenium rc and web driver is named as Selenium2 .
To Learn about how all four components came into existence please click here.