An edge case in software testing refers to a scenario that occurs at the extreme ends of input ranges or operational limits. These cases often lie outside the typical use cases and might not be encountered frequently, yet they can reveal significant issues when handled improperly. Testing for edge cases is crucial for ensuring software reliability and robustness, as they may expose vulnerabilities, crashes, or bugs that affect user experience. Ignoring edge cases can lead to software failures in real-world applications, creating potential risks for users.