A hardware bug is a bug in computer hardware. It is the hardware counterpart of software bug, a defect in software. A bug is different from a glitch which describes an undesirable behavior as more quick, transient and repeated than constant, and different from a quirk which is a behavior that may be considered useful even though not intentionally designed.
Errata, corrections to the documentation, may be published by the manufacturer to describe hardware bugs, and errata is sometimes used as a term for the bugs themselves.