A defect in software testing refers to an error, flaw, failure, or fault in a computer program that causes it to produce an incorrect or unexpected result, or to behave in unintended ways. A programmer can make mistakes or errors while designing and building software, which can lead to flaws in the software, called defects. Defects can occur when the actual result deviates from the expected result while testing a software application or product. Any deviation from the specification mentioned in the product functional specification document is also considered a defect. Defects can be caused by errors in logic or coding, which can result in failure or unpredictable/unanticipated results. Some common types of defects include arithmetic defects, logical defects, syntax defects, multithreading defects, interface defects, and performance defects. Testers can discover defects during the testing phase, and they are reported to the development team for fixing.