debug is a command in DOS, OS/2 and Microsoft Windows (only in 32bit) which runs the program debug.exe (or DEBUG.COM in older versions of DOS). Debug can act as an assembler, disassembler, or hex dump program allowing users to interactively examine memory contents (in assembly language, hexadecimal or ASCII), make changes, and selectively execute COM, EXE and other file types. It also has several subcommands which are used to access specific disk sectors, I/O ports and memory addresses.

Debugging is the process of finding and resolving bugs or defects that prevent correct operation of computer software or a system. Debugging tends to be harder when various subsystems are tightly coupled, as changes in one may cause bugs to emerge in another.