Semolina is a kind of high-protein wheat flour that's used to make pasta. Couscous is produced by rolling semolina dough into tiny balls.
Semolina plays an especially big role in Southern Italian cuisine — it's an ingredient in gnocchi, pasta, and some kinds of focaccia. The word derives from the Italian semolino and the Latin simila, "the finest flour." While the name suggests fineness, semolina is actually a rather coarse flour. Its high protein and gluten content make it ideal for creating a springy, durable pasta dough that holds its shape during boiling.