Overload

OSHA defines overload as operation of equipment above its normal full-load rating, or of a conductor above its rated ampacity, that would cause damage or dangerous overheating if it lasts. A short circuit or ground fault is not an overload. The CPSC gives a plain cause: plugging too many products into one circuit.

A circuit breaker trips to stop an overload before the wire overheats. If one keeps tripping, do not just reset it. Unplug some loads, and call a licensed electrician if it continues. A short circuit is the other common cause. See why a breaker keeps tripping.