A Pringle is a hyperbolic paraboloid. Mel Magazine invited several mathematicians to analyze the delicious geometry of the chip. From Mel:
Theron Hitchman, Professor of Mathematics at the University of Northern Iowa: Usually, the way mathematicians talk about this kind of thing is in an equation, but I think equations tend to scare people off, so, I guess you could say that a hyperbolic paraboloid is a kind of surface that, when cut one way, it looks like parabolas opening down, and if you rotate it 90 degrees, it looks like parabolas opening up[…]
[Software engineer and mathematician Varun] Vachhar: Hyperbolic paraboloids are really interesting. They're my favorite shape actually, and aside from Pringles, they're used a lot in architecture because they're structurally really strong. Many shapes struggle with compression. A flat roof, for example, might buckle from too much weight, but with a hyperbolic paraboloid, the curves prevent buckling, just like how an arch is stronger than a straight beam.[…]
Hitchman: Pringles are all the same shape, which is part of the reason why they stack so well — there's a uniformity to them — but them being hyperbolic paraboloids means they don't move either, they fit nice and snug. Discs could spin or slide off of each other, but this shape nests together nicely.
"We Asked Three Mathematicians To Calculate the Shape of a Pringle" by Brian VanHooker (Mel)