Helium is a noble gas and has atomic number 2. It has the lowest boiling (4.22K) and melting (0.95K) temperatures of all elements. It is inert - only neon is less reactive. It has low solubility, low density, and high thermal conductivity. It is the second most abundant element in the universe, after hydrogen.
Crude helium (50-99% purity) is extracted from natural gas. This product can be refined into Grade-A helium (>99.997%) through separation of remaining methane, nitrogen, and hydrogen.
Categorization of 2012 domestic helium consumption (Source: U.S. Geological Survey):
Helium is used to cool equipment such as superconducting magnets and particle accelerators. Applications include Nuclear Magnetic Resonance Spectroscopy (NMR) and Magnetic Resonance Imaging (MRI).
In rocket engines, helium is often used as a pressurizing agent, pushing the liquid fuel and oxidizer into the combustion chamber. It is also used as a purging gas, by virtue of its inertness and low boiling and melting temperatures.
Its unique attributes make helium useful in creating specific environments that are necessary for a variety of manufacturing processes.
Welding Cover Gas
Helium is used as a shielding gas in welding processes such as gas metal arc welding, where, due to its inertness, it prevents contamination from other atmospheric gases.
Helium is the smallest atom and has a high diffusion coefficient, making it ideal for testing for leaks. If any leaks are present, helium will pass through and thus expose them.
In deep-water diving, the high pressure makes breathing in regular air problematic. Mixtures containing helium are easier to consume in such circumstances.
Other (lifting gas)
The primary application in the "Other" category is the use of helium as a lifting gas. Because its density is lower than air, helium fills balloons and airships/ aerostats.
The Federal Helium Program, introduced in 1925, was conceived primarily as a means of ensuring that sufficient helium would be available defense purposes, in particular the production of military airships. Until 1960, the Bureau of Mines was the only domestic producer of helium. In response to growing demand for helium, the Helium Act was passed in 1960 in order to incentivize private production of helium and subsequent sale to the government. Helium was accumulated in the Federal Helium Reserve. Congress determined in 1996 that demand for helium had not kept up with projections, and therefore moved to sell off its reserves by 2015 and gradually move toward privatization. (Source: Bureau of Land Management)
Because of the 2015 deadline and the large surplus of helium in the reserve, the reserve helium was sold off at unnaturally low prices. Many believe that these circumstances led to excessive spending of helium - it was not treated as the scarce resource that it is. Now, as the reserve approaches its end, prices are on the rise, yet private production has not yet come in to replace the supply provided until now by the reserve. Thus, the period of transition to privatization is marked by a shortage of helium. And, while private production will gradually develop, it will not change the fact that the supply of helium is in general quite limited on earth, and that demand for helium may quite possibly outpace supply in the foreseeable future.