tortillas
Thin flatbreads made from corn masa or wheat flour, cooked on a griddle; in Mexico the word usually means corn tortillas.
Wheat tortillas are sold as wraps in nearly every supermarket, while proper corn tortillas made from nixtamalized corn are more likely found in Latin American shops, well-stocked delis, the freezer section or by mail order. To make them yourself you need masa harina, available through the same channels.
Substitute:
Wheat tortillas work at a pinch but are softer, blander and lack the characteristic corn flavour; ordinary cornmeal or polenta will not make corn tortillas, because without nixtamalization it does not form a dough that holds together.