What Vietnamese fermented fish sauce is called nước mắm?

The Vietnamese fermented fish sauce called nước mắm is a foundational seasoning in Vietnamese cuisine.

Nước mắm is traditionally made by fermenting fish—often anchovies—with salt. The mixture is aged in large wooden barrels or other containers, allowing enzymes and microorganisms to break down the fish into a clear, savory liquid rich in umami. The first liquid drawn from a fermentation batch is generally regarded as the highest-quality portion.

Nước mắm is used both as a cooking ingredient and as a table condiment. It may be served plain or diluted and blended with ingredients such as sugar, lime juice, garlic, and chili to make nước chấm dipping sauce. It is sometimes confused with mắm ruốc, a thicker fermented shrimp paste, but the two are distinct products. Phú Quốc and Phan Thiết are especially well-known Vietnamese fish-sauce-producing regions.