What are atoms in Erlang?

An atom is a constant whose only value is its own name — think of it as a symbolic label rather than a variable. Atoms are written lowercase (ok, error, undefined) or quoted if they contain spaces or start with a capital ('My Atom').

They're used everywhere as tags: function results like {ok, Value} or {error, Reason}, process states, and message types all lean on atoms so the receiving code can pattern-match on a clear, self-documenting label instead of a raw number or string.

Atoms are stored once in a global atom table and compared by reference, so matching on them is essentially an integer comparison — fast, regardless of how long the atom's name is.

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