Definition of "plys"

Quality specifications for plywood subfloor material are such that only the outside plys are knot-free.

1963, Materials Research and Standards, volume 3, page 67

Panels may range in thickness from 1/8" to 11/2", containing as few as three plys or as many as fifteen.

1962, MotorBoating, volume 109, number 4, page 154