Masa is a cornmeal dough made by soaking dried field corn in a lime solution, then grinding it into a fine paste. This paste or Masa is made into tortillas, tamales, and sweet fried foods.
Masa is available fresh or dried (Masa Harina), although many cooks believe that fresh Masa has a better taste and texture.
Do not substitute corn meal or regular corn flour. They are made from different types of corn and are processed differently, thus will not be able to produce the same results.