A persistent error in software or hardware. If the bug is in software, it can be corrected by changing the program. If the bug is in hardware, new circuits have to be designed.

Although the derivation of bug is generally attributed to the moth that was found squashed between the points of an electromechanical relay in a computer in the 1940s, the term goes back to the 1800s to refer to flaws in mechanical systems. See buggy, bug fix, software bug, broken and Web bug. Contrast with glitch.

A Note from the Author

On October 19, 1992, I found my first "real bug." When I fired up my laser printer, it printed blotchy pages. Upon inspection, I found a bug lying belly up in the trough below the corona wire. The printer worked fine after removing it!