Couscous is a small, granular pasta made by rubbing semolina (coarse durum wheat flour) with water into tiny pellets, then steaming them until light and fluffy. It has been a staple of Berber and North African cooking for centuries, most closely associated with Morocco, Algeria, and Tunisia, and traditionally rolled by hand rather than extruded like other pasta.
In cooking, couscous is steamed and fluffed, typically as a bed for stews and tagines or seasoned on its own with olive oil, herbs, nuts, and dried fruit. It absorbs the flavor of whatever it's served with rather than asserting much flavor of its own.
Couscous is sold in several sizes: fine Moroccan-style couscous with tiny grains, the larger pearl-shaped Israeli (or pearl) couscous with a chewier bite, and coarser Lebanese-style couscous. Sizing changes both texture and cooking time, so recipes calling for one type aren't interchangeable with another without adjusting liquid and timing.