Heli is a term that can refer to various concepts, but it is often associated with helicopters or the prefix "heli-" which denotes something related to the sun, such as in heliocentric models. Helicopters are versatile aircraft that can take off and land vertically, making them useful for various applications, including transportation, medical emergencies, and military operations. In the context of helium, Heli is also a shorthand for the element, which is a colorless, odorless gas that is lighter than air. Helium is commonly used in balloons, as well as in scientific applications like cryogenics and as a cooling medium in nuclear reactors.