The Selenium Remote Controller (RC) or Selenium Server acts as an HTTP proxy, intercepting and verifying HTTP messages passed between the browser and the application under test. Selenium RC Launches and closes browsers, interprets and runs the Selense commands passed from the test program. Test programs could be .Net, Java, Ruby, Python or other supported languages.
Client libraries for each programming language provide the interface between each programming language and the Selenium RC Server.
Selenium RC Architecture:
Photo Courtesy : http://seleniumhq.org/