What is the difference between a bug and a defect?

In software testing, a "bug" is a specific instance of an error that causes a program to behave unexpectedly or produce incorrect results. It is usually identified during testing and reported with details such as steps to reproduce and expected vs actual outcomes. A "defect" is a broader term that refers to any deviation from the specified requirements or standards, which can include bugs, design flaws, missing features, or performance issues. Essentially, a bug is a type of defect that manifests as a malfunction in the code, while a defect encompasses all kinds of non‑conformance, including bugs, usability problems, and documentation errors.