bug

A programming error that causes a software application or computer system to perform erratically, produce incorrect results, or crash altogether.

Historical perspective: The term "bug" came from the world's first computer --the ENIAC, more specifically the Mark 1-- which was a room-size maze of electromechanical circuits built in 1944 in a lab at Harvard University. The computer developed a glitch one day, and no one was able to locate the cause. After hours of searching, a lab assistant finally spotted the problem: A moth had landed on one of the computer's circuit boards and shorted it out. From that moment on, computer glitches were referred to as bugs, even though in modern usage, "bug" refers to a software problem and "glitch" refers to a hardware problem.