To coagulate means to change from a liquid into a thicker, semi-solid state. When you get a cut on your finger, your blood coagulates, forming a clot that stops the bleeding and eventually becomes a scab. Without this coagulation, even a small cut would keep bleeding.

Coagulation happens through chemical changes in a liquid. When you cook an egg, the clear, runny egg white coagulates into a firm white solid because heat changes the proteins inside. When you make cheese, adding special enzymes causes milk to coagulate, separating into solid curds and liquid whey.

Scientists study coagulation in blood to help people with clotting disorders. Chefs use coagulation when making custards, puddings, and other dishes that need to set.

You might see the related word coagulant, which is a substance that causes coagulation, like the rennet used in cheese making or the chemicals that help purify drinking water by making impurities coagulate and settle out.