In computing technology, a bug is an unintentional coding error in a computer application program, hardware device or operating system. Bugs can typically cause annoying computer glitches, or cause more serious problems including life-threatening situations. In 2018 and 2019 a bug in the sensor on the Boeing 737 Max caused Lion Air Flight 610 and Ethiopian Airlines Flight 302 to crash.

Because bugs are unwanted in computer code they need to be found and fixed in a process called debugging.