Selenium is a set of tools designed to automate browsers. It is commonly used for web application tests across multiple platforms. There are a few tools available under the Selenium umbrella, such as Selenium WebDriver(ex-Selenium RC), Selenium IDE and Selenium Grid.
WebDriver is a remote control interface that enables you to manipulate DOM elements in web pages, as well as to command the behaviour of user agents. This interface provides a language-neutral wire protocol which has been implemented for various platforms such as:
as well as other implementations:
Selenium WebDriver is one of the Selenium tools which provides Object Oriented APIs in a variety of languages to allow for more control and the application of standard software development practices. To accurately simulate the way that a user will interact with a web application, it uses "Native OS Level Events" as oppose to "Synthesized JavaScript events".
Links to refer: