The article provides a comprehensive overview of Selenium, a leading test automation framework for web applications, focusing on the differences between Selenium Standalone Server and the legacy Selenium Server. Selenium supports various programming languages and integrates with frameworks like JUnit and TestNG, enhancing test management. The latest version, Selenium 4, introduces new features that improve testing processes. Selenium components, such as Selenium IDE, WebDriver, and Grid, each serve distinct purposes like recording, executing in different browsers, and managing parallel test executions across multiple machines. The Standalone Server facilitates distributed test execution, offering benefits like cross-browser testing and parallel execution, while overcoming limitations of local grid setups with cloud solutions like LambdaTest. In contrast, the legacy Selenium Server, now deprecated, was primarily used with Selenium Remote Control for executing scripts in a single browser. Understanding these components is crucial for effective Selenium Grid usage, either locally or via cloud grids.