Neutrons are neutral subatomic particles found in the nucleus of an atom, alongside protons. They play a crucial role in the stability of atomic nuclei, as they help to offset the repulsive forces between positively charged protons. The number of neutrons in an atom can vary, leading to different isotopes of the same element, which can have unique properties. Discovered in 1932 by James Chadwick, neutrons are essential for various nuclear reactions, including fission and fusion. Their presence is vital in the functioning of nuclear reactors and the creation of energy in stars. Understanding neutrons is key to advancements in both nuclear energy and medical applications like radiation therapy.