What is the difference between Selenium IDE, selenium Webdriver and selenium Grid?

Selenium IDE : The Selenium IDE is basically something having record & playback options which present in the every automation tool like QTP, Sliktest etc. & also has very good user interface.

Selenium WebDriver : It supports with all browsers like Firefox, IE, Chrome, Safari, Opera etc.It doesn’t supports Record and playback.Doesn’t required to start server before executing the test script.It actual core API which has binding in a range of languages.