Defect

A Defect is an imperfection, flaw, or fault in a software product that causes it to deviate from its intended functionality or requirements. It's the technical error or bug in the code that can lead to a failure when executed under specific conditions.

Example: A defect exists in a login feature's code where a case-sensitive check is incorrectly applied to usernames. As a result, a user with the username "JohnDoe" cannot log in using "johndoe." The defect is the faulty code itself, and the failure is the user's inability to log in.