贝类 (bèi lèi) literally means 'shell category' — 贝 (bèi) refers to shells or shellfish, and 类 (lèi) means 'kind' or 'category'. Together, they form a scientific and general term for mollusks: soft-bodied invertebrate animals, many of which have hard external shells, such as clams, oysters, mussels, scallops, squid, and octopuses. Though the character 贝 originally evokes shelled creatures, in modern usage 贝类 includes both shelled (e.g., clams) and unshelled (e.g., squid) mollusks.

This term is widely used in biology, food labeling, seafood markets, and environmental discussions. It’s more formal and inclusive than colloquial terms like 海鲜 (hǎixiān, 'seafood') and carries no culinary connotation by itself — it simply classifies a biological group. In daily speech, people often specify individual types (e.g., 牡蛎, mǔlì — oyster), but 贝类 serves as the umbrella noun when discussing taxonomy, safety (e.g., contamination warnings), or dietary guidelines.