A clot is a thick lump that forms when a liquid thickens and sticks together. The word usually refers to blood that has changed from liquid to a sticky, gel-like mass.

When you cut your finger, blood flows out at first. But soon your body performs something remarkable: special cells called platelets rush to the wound and stick together, forming a clot that plugs the opening like a cork in a bottle. This clot stops the bleeding and protects the wound while it heals. Underneath that crusty scab on your knee is a blood clot doing its job.

Clots can form in other liquids too. Milk can clot when it spoils. Gravy can clot when it gets cold and lumpy. Paint can clot in the can if you don't stir it properly.

Sometimes the body forms clots when it shouldn't, like inside blood vessels where blood needs to keep flowing smoothly. Doctors work to prevent these dangerous clots because they can block blood flow to important organs.

The word can also mean a foolish person in British English, though this usage is much less common. When something clots, it thickens and forms lumps instead of staying smooth and liquid.