When end-user-visible behavior deviates from the expected behavior, this situation is called what?

The situation where end-user-visible behavior deviates from the expected behavior is referred to as a failure. This term specifically describes the manifestation of an error in the software, resulting in an observable incorrect behavior from the user's perspective. While errors, faults, and defects relate to issues in the software development process, they do not necessarily result in visible discrepancies that a user could directly observe.

When a failure occurs, it indicates that the software did not perform as intended, leading to a negative experience for the end-user. This is critical for testers and stakeholders as it highlights the impact of issues on user satisfaction and helps identify areas needing improvement or correction in the software. Understanding failures can inform better testing strategies, enhance quality assurance practices, and ultimately lead to a more reliable product for users.