supercritical

Imagine heating a substance until it reaches a special limit called the critical point. If you go beyond that limit, it becomes supercritical. In science, this often means a state where a substance is no longer clearly a liquid or a gas and starts to act like both. In nuclear science, it means a chain reaction is growing rather than staying steady. Outside technical fields, people sometimes use the word more loosely for something that has gone beyond an important limit or has become very important, but that use is less exact.

"Supercritical" is a term mainly used in science for something that has gone beyond a critical point or limit. In physics and chemistry, a supercritical fluid exists above its critical temperature and pressure. In that state, the substance is no longer clearly divided into liquid and gas phases. It can spread through materials like a gas while also keeping some useful density like a liquid. Because of this, supercritical carbon dioxide is used in processes such as decaffeinating coffee and extracting oils.

In nuclear physics, the term has a related but more specific meaning. A reactor or mass is supercritical when each round of fission leads to more than one further fission on average, so the chain reaction increases. This is different from a critical state, where the reaction simply keeps itself going at a steady rate. A supercritical state may be controlled, as in a reactor that is raising power, or uncontrolled, which is why the distinction matters.

Outside science, "supercritical" is sometimes used in an extended way for a situation that has passed an important limit or become highly serious. For example, someone might speak of a supercritical stage in a project or a supercritical moment in a crisis. This figurative use is understandable, but it is much less standard than the scientific one. Most of the time, the word points to a technical state beyond a defined critical threshold.