Usable security is security guidance and security controls that people can understand and follow in real situations. It focuses on clarity, timing, and fit: a warning, login prompt, or recovery step should be easy to interpret when the user is rushed, distracted, or unsure. If a control is confusing or too hard to complete, people often ignore it, work around it, or make unsafe choices.
This matters because many attacks succeed through social engineering rather than technical breakage. Phishing emails, fake login pages, and misleading support messages exploit confusion and pressure. Defenses such as clear MFA prompts, recognizable account warnings, readable language, and safe default settings improve the chance that users notice danger and act correctly. In practice, usable security treats human behavior as part of the security design, not an afterthought.