Non-inflammable, lighter-than-air, inert gas.
A very light colorless element that is one of the six inert gasses; the most difficult gas to liquefy; occurs in economically extractable amounts in certain natural gases (as those found in Texas and Kansas); SYN. He, atomic number 2.
Colorless, odorless, gaseous, nonmetallic element, symbol He, atomic number 2, atomic weight 4.0026. It is grouped with the inert gases, is nonreactive, and forms no compounds. It is the second-most abundant element (after hydrogen) in the universe, and has the lowest boiling (-268.9şC/-452şF) and melting points (-272.2şC/-458şF) of all the elements. It is present in small quantities in the Earth's atmosphere from gases issuing from radioactive elements (from alpha decay) in the Earth's crust; after hydrogen it is the second-lightest element.
Helium is a component of most stars, including the Sun, where the nuclear-fusion process converts hydrogen into helium with the production of heat and light. It is obtained by compression and fractionation of naturally occurring gases. It is used for inflating balloons and as a dilutant for oxygen in deep-sea breathing systems. Liquid helium is used extensively in low-temperature physics (cryogenics).