Plain English Meaning
What the airplane itself weighs when it is sitting on the ramp with nothing loaded into it -- no people, no bags, and no usable fuel. Just the aircraft and the things permanently attached to or built into it.
Full Definition
The weight of the airframe, engines, all permanently installed equipment, and unusable fuel. Depending on the manufacturer's standard, empty weight may also include full operating fluids such as engine oil, hydraulic fluid, and engine coolant. It does not include the pilot, passengers, baggage, or usable fuel.
Context Anchor
Seen in weight-and-balance calculations, the aircraft’s current weight-and-balance record, and the loading section of the Pilot’s Operating Handbook.