海狮是属于海狮科的海洋哺乳类动物，统合为海狮亚科。

耳朵小；纺锤状般的流线身体，可在水中灵活运动，前后肢呈鳍状、后肢能转向前方以支持身体，以及能够利用鳍足在平地上走动；身体被有粗毛；雄性长2.5-3.25米，随种类而异，雌性较小；有外耳廓（相对于没有外耳廓的海豹科）。因为有的种类雄性海狮颈部有长毛似狮，故名。

多数人易将海狮、海豹和海象搞混，但这3种动物分辨方式简单，有着小小外露的耳朵是海狮；没有外露耳朵是海豹；体型巨大，有长长獠牙的是海象。海狮体型较小，体长一般不超过2米。北海狮为海狮科最大的一种。雄性体长310-350厘米，体重1000千克以上。雄性成体颈部周围及肩部生有长而粗的鬃毛，体毛为黄褐色，背部毛色较浅，胸及腹部色深。雌性体色比雄兽淡，没有鬃毛。面部短宽，吻部钝，眼和外耳壳较小。前肢较后肢长且宽，前肢第一趾最长，爪退化。后肢的外侧趾较中间三趾长而宽，中间三趾具爪。

Sea lions are sea mammals characterized by external ear flaps, long foreflippers, the ability to walk on all fours, and short, thick hair. Together with the fur seals, they comprise the family Otariidae, eared seals, which contains six extant and one extinct species (the Japanese sea lion) in five genera. Their range extends from the subarctic to tropical waters of the global ocean in both the Northern and Southern Hemispheres, with the notable exception of the northern Atlantic Ocean. They have an average lifespan of 20–30 years. A male California sea lion weighs on average about 300 kg (660 lb) and is about 8 ft (2.4 m) long, while the female sea lion weighs 100 kg (220 lb) and is 6 ft (1.8 m) long. The largest sea lion is Steller's sea lion, which can weigh 1,000 kg (2,200 lb) and grow to a length of 10 ft (3.0 m). Sea lions consume large quantities of food at a time and are known to eat about 5–8% of their body weight (about 15–35 lb (6.8–15.9 kg)) at a single feeding.