Corrugated means molded into tight ridges and valleys. You've probably seen corrugated cardboard, or corrugated metal roofs.
Materials are put into a corrugated shape to ensure elasticity and strength––cardboard boxes hold their shape because the cardboard is reinforced with a corrugated layer inside the two flat pieces. To remember corrugated, think about corduroy pants––which also have ridges and valleys. If you're lucky enough to have had ribbon candy, that's corrugated as well.
