Selenium Grid allows you to run multiple instances of Selenium Remote Control in parallel concurrently and makes them appear as one.
By leveraging your existing computing infrastructure, it allows you to run multiple functional tests in parallel, on multiple machines, against different browsers, in a heterogeneous environment.
Selenium Grid can be used to execute same or different test scripts on multiple platforms and browsers concurrently so as to achieve distributed test execution, testing under different environments and saving execution time remarkably.