A sardine is a small, silvery ocean fish, usually between three and six inches long. The word actually refers to several different species of small fish, but they all share that same compact, streamlined shape. Fresh sardines have soft, edible bones and oily, flavorful meat.

Most people know sardines from the distinctive flat metal tins you see stacked in grocery stores. Workers pack the cooked fish tightly into these cans, which gave rise to the expression packed like sardines. When people squeeze into a crowded elevator or cram into the back seat of a car with barely any room to move, they might joke that they're “packed like sardines.” The phrase captures that feeling of being pressed against others in an uncomfortably tight space.

Sardines were historically an important food because the canning process preserved them for months or even years without refrigeration. Fishermen could catch huge schools of sardines (they swim together in massive groups), can them on factory ships, and transport them anywhere in the world. Today, sardines remain popular in many cuisines. Some people eat them straight from the tin, while others cook them fresh on a grill. They're especially beloved in Portugal, Spain, and Mediterranean countries, where street vendors sell them hot off the grill during summer festivals.