Salted shrimp
Tiny shrimp packed in plenty of salt and fermented, a very salty, savoury paste with the small shrimp still whole.
Saeujeot are very small, pale shrimp packed raw in generous amounts of salt and fermented for months. They taste intensely salty with a deep, slightly sweet sea flavour that softens and rounds out with cooking. In Korean cooking they are used mainly as a seasoning, for kimchi, steamed egg, soups and as a dip for boiled pork, and usually only by the spoonful. You can find them in Asian grocery shops, mostly in jars or tubs in the chilled section or frozen, and by mail order. Once opened, a jar keeps for a long time in the fridge and practically indefinitely in the freezer.
Substitute:
Fish sauce is the usual stopgap, especially in kimchi and soups: it supplies salt and umami, but tastes of fish rather than shrimp and leaves no small pieces in the dish. As a dip for pork there is no workable substitute, because the flavour and bite of the whole shrimp are the point there.