Cornbread is made from cornmeal, but what are corn tortillas made from? That would be masa harina, a finely ground preparation of corn flour, or "dough flour," says Uncle Bob. "Field corn (not sweet) is dried and then treated/soaked in a solution of lime and water," says Uncle Bob. "This loosens the hulls from the kernels and softens the corn. The soaked corn is then washed, and the wet corn is ground into a dough, called masa. It is this fresh masa (dough), when dried and powdered, that becomes masa harina (dough flour)." This is what's used in making tortillas and tamales; the treatment of the corn gives the final dish its characteristic flavor. paulj notes that there are several "grinds" of masa harina. The stuff for tortillas is a much finer grind than the stuff used in tamales.
In addition, to make matters even more confusing, there's a flour made from cooked corn that is used in arepas, a type of corn cake made in Colombia and Venezuela, says paulj. "Goya brand Masarepa is what you want for arepas," says bushwickgirl. "It's a precooked corn flour and it has a unique taste. I'm sure there are other brands available, but this is the one I can find most readily and use."