WebDriver:
WebDriver object represents the browser in Selenium.
Using this object you can control the Web browser.
It is an interface of the org.openqa.selenium.* package.
Upon instantiating the implementations of this class
the browser will be launched.
FirefoxDrive, ChromeDriver,
InternetExplorerDriver, SafariDriver, OperaDriver,
HtmlUnitDriver, RemoteWebDriver are few
implementations of the WebDriver Interface.