Definition
The structural beam running spanwise (from root to tip) along the rear portion of a wing or stabilizer, carrying bending and torsional loads and serving as an attachment point for control surfaces such as ailerons, flaps, or elevators.
Plain English
A long, strong beam inside the back part of a wing or tail surface. It helps the wing hold its shape under load and gives the moving control surfaces something solid to hinge from.
Context Anchor
Seen in aircraft structure descriptions, especially when reading about how an adjustable stabilizer is built and attached.
Derivation
Spar comes from an old word for a wooden pole or beam, the same root used for ship masts and yards. Early aircraft borrowed shipbuilding language, and 'rear' simply identifies which of the two main spars in the wing is being referred to — the one toward the trailing edge.
Why Pilots Care
The rear spar forms the structural backbone that keeps the tail rigid and allows the elevator to move safely for pitch control.
Intuition Check
Do not read rear spar as just any part at the back of the airplane. It is a specific internal structural beam near the back of a wing or stabilizer.
Example Sentence 1
On this aircraft, the adjustable stabilizer pivots on the rear spar, allowing its angle of incidence to be changed in flight.
Example Sentence 2
The elevator hinges attach directly to the rear spar of the stabilizer.