Selenium is a suite of tools for automating web browsers, often used for testing web applications and scraping dynamic websites. It provides a framework for controlling and interacting with web browsers programmatically through various languages such as Python, Java, and JavaScript. Selenium can simulate user interactions like clicking, typing, and navigating, making it ideal for scraping content from websites that require user input or load data dynamically with JavaScript. It includes components like Selenium WebDriver, Selenium Grid, and Selenium IDE, each serving different purposes in web automation and testing.