Boil

Technically, the point at which a liquid changes into a gas (or vapor) is its boiling point. For cooking purposes, liquid has come to a boil when bubbles form uniformly across the surface; when the bubbles are so vigorous they cannot be stirred down, it is called a hard, rolling boil. Reduction sauces, pasta, and crisp cooked vegetables, for example, are always cooked at a hard, rolling boil.