Selenium WebDriver
Selenium WebDriver is the core browser-automation API within the Selenium project — a protocol and set of language bindings that let test code control a real browser directly (clicking, typing, navigating) as if a user were doing it, without needing a separate recording or playback layer.
WebDriver replaced Selenium's earlier, JavaScript-injection-based approach (Selenium RC) with direct, native control of the browser through each browser's own automation APIs — a more reliable, less hacky foundation that also became the basis of the official W3C WebDriver standard.
"Selenium" and "Selenium WebDriver" are often used interchangeably today, since WebDriver has been the dominant part of the Selenium project for over a decade — Selenium Grid (for distributing tests across machines) and Selenium IDE (a browser extension for recording tests) are the other notable pieces of the broader project.
