Wikipedia
Crinkle-cutting
Crinkle-cutting is slicing that leaves a corrugated surface. This is done with corrugated knives or mandoline blades.
Crinkle-cut potato chips are sometimes called ruffled, by analogy with a ruffle in sewing. French fries or sweet potato fries may also be crinkle-cut, and may be called "wavy fries".
If the potato is turned 90° between cuts, the result is waffle fries.