It's a term peculiar to the aviation industry and refers to the leasing of an aircraft to an airline, along with a crew to fly the plane and provide the onboard service. Straightforward leasing of an aircraft is usually referred to as dry leasing while wet leasing can be thought of as coming with a drink!

The term "wet lease" in the aviation and shipping industries refers to a leasing arrangement where one organization (the lessor) provides an aircraft, complete crew, maintenance, and insurance (ACMI) to another organization (the lessee). The "wet" part of the name is a historical metaphor derived from the idea that the vehicle comes "with all its fluids," specifically fuel, although in modern aviation, the fuel is usually paid for by the lessee. It implies that the lessor is providing everything necessary to operate the flight immediately, essentially "thawing out" or "moistening" a dry asset into a functional service. This is contrasted with a "dry lease," where only the physical aircraft is provided without crew or operational support. Wet leases are frequently used by airlines to cover sudden spikes in demand, seasonal routes, or unexpected maintenance issues with their own fleet, allowing them to maintain their schedule without the long-term commitment of hiring new staff or purchasing additional planes.