A module is a self-contained component of a system, which has a well-defined interface to the other components; something is modular if it is constructed so as to facilitate easy assembly, flexible arrangement, and/or repair of the components.

• For modules in the architecture sense, see Vitruvian module.
• For modules in computer programming see module (programming) (see also Modularity (programming))
• For modules in the Linux operating system kernel, see module (Linux).
• In mathematics, there are a number of unrelated concepts which use the words module or modular. In abstract algebra, see module (mathematics). In complex analysis, see modular form. In representation theory, see modular representation theory.
• For modules as a computer-generated music filetype (.mod) see module_file.
• For hypothesized modules in mental processes, see modularity of mind.