A soft-boiled egg is an egg cooked briefly in its shell so the white sets while the yolk stays runny. It's typically lowered into simmering water for about 6-7 minutes, timing that varies with egg size and desired yolk firmness; the earliest documented soft-cooked eggs come from ancient Rome, where they were served with a sauce of pine nuts, pepper, vinegar, and honey.
The dish is best known today as a British breakfast: served upright in an egg cup with the top sliced off, eaten by dipping strips of toast ("soldiers") into the yolk. France (oeuf à la coque) and other European countries have their own versions, usually served as part of a breakfast spread with bread, cheese, and cured meat.
Related preparations include the "jammy" egg (a slightly firmer yolk) and the Japanese onsen egg, slow-cooked in hot spring water to a custard-like set. Soft-boiled eggs are also used to top salads and asparagus, or in dishes like eggs Benedict.