is that torus is (topology) a topological space which is a product of two circles while doughnut is a deep-fried piece of dough or batter, commonly of a toroidal (a ring doughnut ) often mixed with various sweeteners and flavourings; or flattened sphere (a filled doughnut) shape filled with jam, custard or cream.

What is a donut called in math?

Torus. A torus is the mathematical name for a doughnut shape or rubber ring shape and is hollow inside.

What is special about a torus?

The torus is the only surface which can be endowed with a metric of vanishing curvature. It is the only parallelizable surface. It is the only surface which can be turned into a topological group.