A supercritical fluid (SCF) is any substance at a temperature and pressure above its critical point, where distinct liquid and gas phases do not exist. It can effuse through solids like a gas, and dissolve materials like a liquid. In addition, close to the critical point, small changes in pressure or temperature result in large changes in density, allowing many properties of a supercritical fluid to be "fine-tuned". The fluid will also be called supercritical even if its temperature is below critical point value.[citation needed] In that case, it will be a highly compressed liquid. But pressure is mandatory to be above the critical value.