Functional Testing
In plain terms
Verifying that features work as specified.
Going deeper
Functional testing checks that the software's functions produce correct outputs for given inputs, focusing on what it does, not how. It validates behavior against requirements.
Under the hood
Black-box in nature; complements non-functional testing (performance, security).
Examples
Feature verification, input/output checks, requirement-based tests, black-box testing.
Think of it like...
Like checking that every button on a remote does exactly what its label says.