Usability measures how easily people can use a designed product to achieve their goals. A door handle that invites pulling when it needs pushing fails usability. A checkout flow that hides the payment button frustrates users. The term comes from human factors research and became central to software design in the 1980s and 1990s, when Jakob Nielsen and others published heuristics for evaluating interfaces.

Usability has several dimensions. Learnability: how quickly a new user can accomplish basic tasks. Efficiency: how fast an experienced user can work. Memorability: how well a casual user remembers the interface after time away. Error rate: how often users make mistakes and how easily they recover. Satisfaction: how pleasant the experience feels. A product can score well on some and poorly on others. A complex professional tool might be efficient but hard to learn.

Common usability principles

• Visibility of system status.
• Match between system and real world.
• User control and freedom.
• Consistency and standards.
• Error prevention and clear recovery.

Usability testing is simple in principle. Watch real people try to use the product. Take notes. Fix what confuses them. Repeat.