A debugger is a software tool used by programmers to identify and fix errors, or "bugs," in their code. It allows developers to run their programs step by step, examine variables, and monitor the flow of execution. This helps in understanding how the code behaves and where it might be going wrong. Debuggers often provide features like breakpoints, which pause the program at a specific line, and watchpoints, which track changes to variables. Popular debuggers include those integrated into development environments like Visual Studio and Eclipse, making it easier for developers to create reliable software.