A consult is a request by an attending physician that a specialist review part or all of the patient's medical records to provide an opinion. However, the attending is not bound by the specialist's advice and is still responsible for the care of the patient.
Hospitals usually have an "on-call" list for consults in each medical speciality at any time, particularly outside regular hospital hours.
Gregory House occasionally does get called for consults, but since he ignores most of the requests, most of the doctors at the hospital don't even bother asking.
House often goes to James Wilson for "consults" that are actually just an excuse for him to drop by Wilson't office for a chat.