Atom may refer to one of the following:
In mathematics, an element which is minimal among non-minimal elements (in a preorder or poset). Related notions may be found at atom.
In set theory, there are theories (for example ZFA) which admit urelements, which are also called atoms.
In physics, a basic unit of matter that represents a chemical element or one of its isotopes, consisting of a central nucleus of protons and neutrons and a “cloud” of electrons surrounding it. See atom (physics)?.