What is the difference between Selenium IDE, Selenium RC and Selenium WebDriver?

Selenium IDE is a Firefox or Chrome plugin that allows you to record and run the tests which you run using Firefox. You can not perform advanced testing strategies in IDE like looping a single action for several times etc because you cant use any programming language to write the test cases.

Selenium RC and WebDriver allows you to choose a language of your interest to write the test cases. with the help of Selenium RC or WebDriver, you can perform almost any kind of action, which you do manually. The major difference between RC and WebDriver is, RC uses a remote control to convert your tests into browser native code, your tests interact with the Remote control and the remote control interacts with the browser where as WebDriver directly interacts with the browser without any Remote server, so the execution is faster.

I read somewhere that RC converts the test cases which are written in some programming language into Javascript functions ( which can control the browser) where as Web Driver communicates with the browser directly through HTTP commands.

Selenium RC is deprecated and people are using WebDriver instead of RC.

Selenium is an open-source project that can be read in more detail here.

Selenium IDE is a browser plugin (currently for Chrome and Firefox only). It's easy and used if one wants to script out website interactions like quick bug reproductions. Thing is, it creates very fragile tests that break a lot.

Selenium WebDriver is a programmatic package that drives a browser natively. It's meant to help develop automation that interacts with, primarily, with the frontend of websites. Other tools, like Nightwatch.js, use it as core.

There's differences between the two: while Selenium IDE is good for making these exploratory scripts, Selenium WebDriver is a way to make real production ready system tests.

According to the official documentation at Choosing Your Selenium Tool:

Many people get started with Selenium IDE. If you are not already experienced with a programming or scripting language you can use Selenium IDE to get familiar with Selenium commands. Using the IDE you can create simple tests quickly, sometimes within seconds.

We don’t, however, recommend you do all your test automation using Selenium IDE. To effectively use Selenium you will need to build and run your tests using either Selenium 2 or Selenium 1 in conjunction with one of the supported programming languages. Which one you choose depends on you.

At the time of writing the Selenium developers are planning on the Selenium-WebDriver API being the future direction for Selenium. Selenium 1 is provided for backwards compatibility. (...).

(...) However, for those who are adopting Selenium for the first time, and therefore building a new test suite from scratch, you will probably want to go with Selenium 2 since this is the portion of Selenium that will continue to be supported in the future.

Also from the documentation, note that Selenium 1 is also known as Selenium RC or Remote Control and Selenium 2 is also known as Selenium WebDriver.