The Page Object Model is a design pattern where each page (or component) of the application is represented by a class that encapsulates its locators and interaction methods, so tests interact with pages through a clean API rather than raw locators.
In POM, a LoginPage class holds the page's element locators and exposes intent-revealing methods (login(user, pass), getErrorMessage()). Tests call loginPage.login(...) instead of finding elements directly. This centralizes locators (a UI change updates ONE class, not every test), improves readability (tests read as business steps), and promotes reuse. Best practices: page methods return page objects (enabling fluent chaining) or data, keep assertions OUT of page objects (they belong in tests), and model reusable components (header, modal) as their own objects. POM is the single most-asked framework-design pattern.
When the login button's id changes, only LoginPage.LOGIN_BTN is updated; the 40 tests that call loginPage.login(...) keep working unchanged — the core maintainability win of POM.
Why should assertions live in the test and NOT inside Page Object methods?