Paralichthys olivaceus, commonly known as the Japanese flounder or olive flounder, is a large left-eyed flatfish in the family Paralichthyidae. It is native to the temperate coastal waters of the western North Pacific, particularly around Japan, Korea, China, and the Russian Far East, where it inhabits sandy and muddy seabeds in shallow continental shelf zones. The genus name Paralichthys derives from Greek para (“beside”) and ichthys (“fish”), referring to the flounder's habit of lying parallel to the sea floor. The species epithet olivaceus is Latin for “olive-colored,” describing the typical dark olive to brown coloration of the eyed side of the fish, which provides camouflage against the seabed.

Historically, the Olive Flounder has been an important coastal food fish in East Asia, especially in Japan and Korea. Paralichthys olivaceus is both wild-caught and extensively aquacultured, particularly in South Korea and Japan, where it is one of the most commercially significant farmed marine finfish species. As a food source, Paralichthys olivaceus is prized for its delicate, white, mildly flavored flesh as well as its fatty fin muscle. It is especially valued for raw preparations as its flesh naturally possesses a slightly crunchy texture. In Japanese cuisine, it is known as hirame and commonly served as sashimi or sushi, where its subtle flavor and translucent flesh are appreciated. In Korean cuisine, known as gwangeo, it is frequently served raw in hoe (sliced raw fish) and accompanied by dipping sauces, as well as used in spicy fish stews such as maeuntang. The fish may also be grilled, steamed, or simmered. Because of its lean flesh and relatively low oil content compared to pelagic species, it has a clean taste and adapts well to a range of preparations.

Paralichthys olivaceus contains complete proteins, omega-3 fatty acids such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), vitamin B12 (cobalamin), niacin (vitamin B3), selenium and taurine. As a benthic predator, it may accumulate trace environmental contaminants depending on habitat conditions, though it is generally regarded as a lean, nutritious seafood.