Definition
In a woven fabric or composite reinforcement cloth, the weft is the set of threads (or fibers) that run crosswise — across the width of the fabric, perpendicular to the warp threads which run lengthwise.
Plain English
The weft threads are the ones that go side to side across a piece of woven cloth, crossing over and under the threads that run the long way.
Context Anchor
Seen in aircraft fabric covering, fabric repair, and inspection discussions.
Derivation
From Old English 'wefta', meaning 'that which is woven,' related to the verb 'weave.' Knowing it simply means 'the woven-across threads' helps fix which direction is which on a roll of fabric or cloth.
Why Pilots Care
Proper alignment of weft and warp affects fabric strength and shrinkage on covered aircraft surfaces.
Intuition Check
Do not read weft as just any fabric thread. It specifically means the crosswise thread direction, not the lengthwise direction.
Example Sentence 1
The technician aligned the weft of the fiberglass cloth across the repair area before wetting it out with resin.
Example Sentence 2
Checking the weft direction ensures the fabric has the correct strength properties for flight loads.