What is a module in Erlang?

A module is Erlang's unit of code organization — a single .erl file compiling to one unit that groups related functions under a shared name. The file starts with a -module(Name). declaration matching the filename, and an -export([...]). attribute listing which functions outside code may call.

-module(math_utils).
-export([square/1]).

square(N) -> N * N.

Functions not listed in -export are private to the module. Calling a function in another module uses the Module:Function(Args) syntax, e.g. math_utils:square(4).

Modules can also be hot-swapped: the BEAM can load a new version of a module into a running system while old processes still executing the previous version finish naturally, which underpins Erlang's live upgrade story.

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