WebDriver vs ChromeDriver

Satish’s answer is correct but in more layman’s terms, ChromeDriver is specifically and only a driver for Chrome. WebDriver is a more generic driver that can be used for many different browsers… IE, Chrome, FF, etc.

If you only cared about Chrome, you might create a driver using

ChromeDriver driver = new ChromeDriver();

If you want to create a function that returns a driver for a specified browser, you could do something like the below.

public static WebDriver startDriver(Browsers browserType)
{
    switch (browserType)
    {
        case FIREFOX:
            ...
            return new FirefoxDriver();
        case CHROME:
            ...
            return new ChromeDriver();
        case IE32:
            ...
            return new InternetExplorerDriver();
        case IE64:
            ...
            return new InternetExplorerDriver();
        default:
            throw new InvalidParameterException("Unknown browser type");
    }
}
public enum Browsers
{
    CHROME, FIREFOX, IE32, IE64;
}

… and then call it like…

WebDriver driver = startDriver(Browsers.FIREFOX);
driver.get("http://www.google.com");

and depending on what browser you specify, that browser will be launched and navigate to google.com.