Tofu is made by coagulating soya milk by Calcium sulfate (gypsum) or other coagulants. Because of its protein content it is a very popular ingredient in vegetarian and vegan dishes.
It is available as a fresh or pre-fried variant on Asian markets. The pre-fried one lasts longer in the fridge. You can freeze both kinds. It very easily overtakes flavour of other ingredients.
Recipes with tofu.