Not so long ago students of French were told: don’t expect to find sweet corn in France! The French only grow corn to feed pigs and ducks! That would be maïs (maize) but maïs doux (sweet corn) is now quite popular.
That said, much of the fresh corn on the cob you can buy in France in summer is often more like horse corn rarely worth writing home about, unless you luck out. You can buy sweet corn in tins (Géant vert etc), which the French like to toss on tuna and tomato salads.
An épi de maïs is an ear of corn (or wheat, barley or rye).
But you can buy other corny things: pop corn (maïs élatés or maïs à soufflér) and corn flakes (flocons de maïs or pétales de maïs) and polenta and corn starch (Maïzena or fécule de maïs).
Image by Nutrition, Food Safety & Health