Debugging is the development activity that finds, analyses and fixes defects. Unlike testing, which aims to identify defects in the software, debugging is the process that developers use to locate and correct the errors found during testing. This involves diagnosing the root causes of these defects and making necessary code changes to resolve them. Debugging is a critical part of the development cycle and ensures that the software functions correctly after defects are fixed.
Reference: ISTQB CTFL Syllabus V4.0, Section 1.1.2