Input validation
Also called: Form validation, Field validation
Checking that what the user typed is acceptable before the app uses it.
Definition
Validation checks format, length, required fields and allowed values. It can run on the client (instantly, for good UX) and must also run on the server (for security). Testers try valid, invalid, empty, too long and unusual inputs.
In practice
An email field should reject "anna@" and "anna.com" with a clear message, and accept "anna+shop@example.co.uk".
Learn it in context
Lessons that use this term.