Selenium is a open-source tool used for automating web application testing across different browsers and platforms. It supports multiple programming languages like Java, Python, and C#, making it flexible for testers and developers. With components such as WebDriver, Selenium Grid, and Selenium IDE, it enables efficient test execution and parallel testing. Selenium helps reduce manual effort, improve accuracy, and speed up the testing process. Learning automation with a Selenium Course in Chennai at FITA Academy can help individuals gain practical skills and build a strong career in software testing and quality assurance.