In the context of software development, a 'bug' is a defect or error in the code that causes a program to behave unexpectedly or produce incorrect results. Bugs can arise from various sources, including logical errors, syntax mistakes, or integration issues. They can lead to software crashes, performance degradation, or incorrect outputs, affecting user experience and system functionality. Debugging is the process of identifying, isolating, and resolving these bugs to ensure that software operates as intended. Effective bug tracking and management are critical components of successful software development and maintenance processes.