From LQWiki

Fixing bugs or problems inside a program. This is typically done with the use of a debugger such as gdb. A bug is defined as: A programming error that causes a program to work poorly, produce incorrect results, or crash. (As an interesting aside, the term "bug" was coined when a real insect damaged one of the circuits of the first electronic digital computer, the ENIAC.) A bug is different from a glitch, which refers to a hardware problem and not a software problem.