Celeriac is a vegetable: a kind of celery grown for a large, round, knobbly white root, not for long green stems. The skin is brown and rough; inside it is pale. The taste is like celery — fresh, a bit earthy — and cooks use it in soup, mash, or salad, often cut into thin strips. In shops you may also see the name celery root. Though actually, it is not a different plant family from celery; it is celery bred so the root becomes the part you eat. In Taiwan it is less common than ordinary celery, and you will mostly meet it in Western-style cooking.