Hello Janki, Selenium Grid is a part of the Selenium Suite that specializes in running multiple tests across different browsers, operating systems, and machines in parallel. Selenium Grid is a tool used together with Selenium RC to run tests on different machines against different browsers in parallel. In simple words, it is used to distribute your test execution on multiple platforms and environments concurrently. It allows running test cases in parallel thereby saving test execution time.
Grid employs a Hub-Node architecture where, there is one Hub, which acts as the master and one or more Nodes acting as slaves. Which means, if you have a total of 100 jobs/tests that need to be executed, then the tests can be executed simultaneously in 5 machines, where each machine will be running 20 tests. This would easily save up on a lot of your time in test execution, as we can reduce the execution time to around 1/5th of the total time taken to execute tests on a single machine.