Ampacity,*in the electrical code, refers to the current, measured in amperes, that a conductor (a wire) can carry continuously under the conditions of use without exceeding its temperature rating - in other words, the ampacity of a #14 gauge copper wire intended for residential electrical wiring is 15 Amps because that's the amount of current that the wire can carry without getting too hot. "Too hot" means a temperature that could damage the wire insulation and thus reduce its safety.