An outlet can be any point along a wiring system where current is taken to supply equipment, though in residential electrical work will most commonly refer to a:
Lighting Outlet. An outlet intended for the direct connection of a lampholder or luminaire.
Receptacle Outlet. An outlet where one or more receptacles are installed.
Power Outlet. An enclosed assembly that may include receptacles, circuit breakers, fuseholders, fused switches, buses, and watt-hour meter mounting means; intended to supply and control power to mobile homes, recreational vehicles, park trailers, or boats or to serve as a means for distributing power required to operate mobile or temporarily installed equipment.
Outlet is sometimes used colloquially to refer to what is defined as a receptacle by the National Electrical Code (NEC).