A ply is a
layer of material which has been combined with other layers in order to provide strength. The number of layers is indicated by prefixing a number, for example 4-ply, indicating material composed of 4 layers.
Etymology
The word "ply" derives from the French verb ''plier'', "to fold", from the Latin verb ''plico'', from the ancient Greek verb ''πλέκω''.
[Cassell's Latin Dictionary, Marchant, J.R.V, & Charles, Joseph F., (Eds.), Revised Edition, 1928, p.421]
Examples
*Yarn, where
plying is a spinning technique to combine several fibres.
*Vehicle
tire
A tire (American English) or tyre (British English) is a ring-shaped component that surrounds a Rim (wheel), wheel's rim to transfer a vehicle's load from the axle through the wheel to the ground and to provide Traction (engineering), t ...
s
*
Plywood
Plywood is a material manufactured from thin layers or "plies" of wood veneer that are glued together with adjacent layers having their wood grain rotated up to 90 degrees to one another. It is an engineered wood from the family of manufactured ...
*
Toilet paper
Toilet paper (sometimes called toilet tissue or bathroom tissue) is a tissue paper product primarily used to clean the anus and surrounding anal region of feces after defecation, and to clean the perineal area and external genitalia of ur ...
References
Structural analysis
Structural engineering