Can people use it without getting frustrated? That is usability in one question. The term covers how easily someone can learn, operate, and get value from a designed product. A door that opens the wrong way has poor usability. So does a checkout flow that hides the payment button.

Jakob Nielsen and Don Norman popularized the concept in the 1990s. Nielsen's ten heuristics, including visibility of system status and user control, became a standard checklist for interface designers. The field has since expanded to include accessibility, mobile touch targets, and cognitive load.

Common usability problems

• Buttons that do not look clickable
• Forms that reject input without explaining why
• Navigation that buries important pages
• Text that is too small or too low-contrast to read
• Error messages that blame the user

Usability testing does not require a lab. Five users will surface most major problems. Watching someone struggle with an interface you designed is humbling, but it is the fastest way to find what is broken. The goal is not to make everything obvious to everyone. It is to remove unnecessary friction so people can do what they came to do.