: something that is folded together or that enfolds
a: a bend or flexure produced in rock by forces operative after the depositing or consolidation of the rock
bchiefly British: an undulation in the landscape
: a margin apparently formed by the doubling upon itself of a flat anatomical structure (as a membrane)
: a crease made by folding something (as a newspaper)
Illustration of FOLD
First Known Use of FOLD
In geology, an undulation or wave in the stratified rocks of the Earth's crust. Stratified rocks were originally formed from sediments that were deposited in flat, horizontal sheets, although in some places the strata are no longer horizontal but have warped. The warping may be so gentle that the inclination of the strata is barely perceptible, or it may be so pronounced that the strata of the two flanks are essentially parallel or nearly flat. Folds vary widely in size; the tops of large folds are commonly eroded away on the Earth's surface.