Liquid helium is a state of helium gas that occurs when it is cooled to extremely low temperatures, below -269 degrees Celsius (-452 degrees Fahrenheit). At this temperature, helium becomes a liquid and exhibits unique properties, such as being able to flow without viscosity, which means it can move through tiny openings and around obstacles effortlessly. This remarkable liquid is primarily used in scientific research and technology, particularly in cryogenics, where it cools superconducting magnets in MRI machines and particle accelerators. Its low boiling point makes it essential for maintaining the temperatures needed for various experiments and applications in physics and engineering.