A round, well-marbled muscle from the cow's upper rib section, tender and juicy. Shops sell it mostly as steaks for pan-frying, and also shave it thin for hot pot and barbecue.
Beef-cut term: 眼肉 = the rib-eye muscle (longissimus dorsi), prized for its central 'eye' of well-marbled meat - that round 'eye' shape is exactly what gives the cut its name in both English and Chinese. Compare 西冷 (sirloin) and 菲力 (filet).