Selenium
In plain terms
A tool for automating web browsers for testing.
Going deeper
Selenium drives real browsers programmatically to test web applications across different browsers and platforms. It pioneered browser automation.
Under the hood
WebDriver controls browsers; powerful but slower and flakier than newer tools like Playwright.
Examples
Cross-browser testing, E2E web tests, WebDriver, UI automation.
Think of it like...
Like a robot that clicks and types through your website exactly like a user.