Cabbage, comprising several cultivars of Brassica oleracea, is a leafy green, red (purple), or white (pale green) biennial plant grown as an annual vegetable crop for its dense-leaved heads. It is descended from the wild cabbage (B. oleracea var. oleracea), and belongs to the "cole crops" or brassicas, meaning it is closely related to broccoli and cauliflower (var. botrytis); Brussels sprouts (var. gemmifera); and Savoy cabbage (var. sabauda).

A cabbage generally weighs between 500 and 1,000 grams (1 and 2 lb). Smooth-leafed, firm-headed green cabbages are the most common, with smooth-leafed purple cabbages and crinkle-leafed savoy cabbages of both colours being rarer. Under conditions of long sunny days, such as those found at high northern latitudes in summer, cabbages can grow quite large. As of 2012, the heaviest cabbage was 62.71 kilograms (138 lb 4 oz). Cabbage heads are generally picked during the first year of the plant's life cycle, but plants intended for seed are allowed to grow a second year and must be kept separate from other cole crops to prevent cross-pollination. Cabbage is prone to several nutrient deficiencies, as well as to multiple pests, and bacterial and fungal diseases.