Selenium is a popular open-source framework used for automating web browser interactions. It allows developers and testers to write scripts in various programming languages (such as Java, Python, C#, etc.) to simulate user actions on web pages, including clicking buttons, filling out forms, and navigating through different URLs. 

Selenium is widely used for web application testing, as it provides a reliable and flexible way to automate the testing process. Testers can create automated tests to ensure that web applications work as expected across different browsers and platforms. Additionally, Selenium can be integrated with various testing frameworks and Continuous Integration (CI) tools, making it suitable for agile development environments.

One of the key features of Selenium is its ability to support multiple browsers, including Chrome, Firefox, Safari, Edge, and Internet Explorer. It uses the WebDriver API to interact with browser instances, allowing developers to write cross-browser tests without having to learn the intricacies of each browser's native automation tools.