Definition
In aircraft sheet metal work, to lay out or cut a piece of material so that its edges are at exact 90-degree angles to one another, or to verify that an existing edge, corner, or assembly is at a true right angle.
Plain English
To make sure two edges meet at a perfect right angle, or to mark and cut a part so its corners are exactly 90 degrees.
Context Anchor
Seen in aircraft sheet-metal layout, structural repair, and inspection work where parts must line up accurately.
Derivation
From the Latin 'exquadrare,' meaning 'to make four-sided.' In trade use it came to mean 'true and at right angles,' which is exactly how mechanics use it on the bench today.
Why Pilots Care
Sheet metal patches, doublers, and structural repairs only fit and carry load correctly if the parts are squared during layout. A piece that is even slightly out of square can cause misaligned rivet holes, gaps, or stress concentrations.
Intuition Check
Do not read square here as just a four-sided shape. In this maintenance context, it means a tool or check for a true 90-degree angle.
Example Sentence 1
Before drilling the rivet line, the technician used a combination square to make sure the doubler was square to the stringer.
Example Sentence 2
After installing the new hinge, the mechanic used a square to verify the aileron was squared to the wing.