Yaki Dofu is a Japanese term for firm tofu that has been lightly grilled or broiled on both sides, so that both sides are slightly browned. The grilling also evaporates some water, helping to firm it up the tofu even more.
It used to be made by putting pieces of tofu on skewers and grilling it over a fire. Now it is done under grills or broilers.
Yaki Dofu can be served hot on its own with sauces, or used as an ingredient. It is good for simmering, as it will hold its shape well.
In Japanese, "yaki" means "grilled".