A fixed-wing aircraft is one who's wings are fixed.
I suppose you want a more
in-depth explanation than that.
On
aircraft, the devices that produce
lift are called "
wings." They are constructed so that as they pass through the air, they creat lift. More detail can be found in the
wing node. They pass through the air by being pushed there on an aircraft, by the aircraft's engine - but what pulls the aircraft forward, exactly?
Why, the propellor of course. The propeller is also a wing. It passes through the air by the spinning motion of the
engine, and creates lift - also, because it
powers the aircraft, it is known as
thrust.
The Propeller is not a fixed-wing. It is not fixed. It spins.
The wing on the aircraft is a fixed-wing. It is attached to the aircraft and does not move.
Any aircraft where the main lift-producing device (wings) are attached and do not move, are referred to as fixed-wing aircraft.
Aircraft where the main lift-producing device (wings) are NOT attached and DO move, they are referred to as
ROTARY-wing aircraft. This would include
Helicopters.
Note that aircraft which have slightly moving wings (some high-speed fighters and bombers for example) are called
swept-wing aircraft, and are considered fixed-wing.