Selenium is an open-source automation testing framework primarily used for web applications. It provides a suite of tools that allows testers to automate web browser interactions across different browsers and platforms. Selenium is widely used for automating web testing tasks such as form filling, UI testing, and regression testing. Here's how Selenium is useful in automation testing:

1. Cross-Browser Compatibility Testing: Selenium allows testers to automate tests across different web browsers such as Chrome, Firefox, Safari, and Internet Explorer. This helps ensure that web applications function correctly and consistently across various browsers and versions.

2. Platform Independence: Selenium supports multiple operating systems (Windows, macOS, Linux) and programming languages (Java, Python, C#, etc.). This makes it highly flexible and suitable for diverse software development environments.

3. Reusable Test Scripts: Test scripts written in Selenium can be reused across different projects and environments, saving time and effort in test development and maintenance.

4. Parallel Test Execution: Selenium Grid, a component of Selenium, enables parallel execution of tests across multiple browsers, operating systems, and machines. This helps reduce test execution time and increases testing efficiency.

5. Integration with Testing Frameworks: Selenium can be integrated with various testing frameworks such as JUnit, TestNG, NUnit, and others. This allows testers to organize and manage their test suites effectively, generate test reports, and perform assertions.

6. Support for Web Element Interaction: Selenium provides APIs for interacting with web elements such as text boxes, buttons, dropdowns, etc. Testers can perform actions like clicking, typing, selecting, and verifying the properties and states of these elements.

7. Continuous Integration and Continuous Testing (CI/CT): Selenium can be integrated with CI/CD tools like Jenkins, Bamboo, and Travis CI to automate the execution of tests as part of the software delivery pipeline. This ensures that new code changes are tested automatically, leading to faster feedback loops and better software quality.

8. Regression Testing: Selenium is well-suited for regression testing, where tests are rerun to ensure that new code changes have not introduced unintended side effects or regressions in the application.

Overall, Selenium is a powerful and versatile automation testing framework that empowers testers to automate web testing tasks effectively, improve testing efficiency, and deliver high-quality software products.