ETYM French, from Latin modulus a small measure, dim. of modus. Related to Mode, Model, Modulus, Mold a matrix.
1. A detachable section of a spacecraft.
2. A self-contained unit or item that is used in combination with other units.
3. An assembly of electronic components (as of computer hardware).
Unit of measurement or means of measuring; standard or self-contained unit of construction; self-contained section of educational course.
In construction, a standard or unit that governs the form of the rest. For example, Japanese room sizes are traditionally governed by multiples of standard tatami floor mats; today prefabricated buildings are mass-produced in a similar way. The components of a spacecraft are designed in coordination; for example, for the Apollo Moon landings the craft comprised a command module (for working, eating, sleeping), service module (electricity generators, oxygen supplies, maneuvering rocket), and lunar module (to land and return the astronauts).

1. In programming, a collection of routines and data structures that performs a particular task or implements a particular abstract data type. Modules usually consist of two parts: an interface, which lists the constants, data types, variables, and routines that can be accessed by other modules or routines; and an implementation, which is private (accessible only to the module) and which contains the source code that actually implements the routines in the module. See also abstract data type, information hiding, Modula-2, modular programming.
2. In hardware, a self-contained component that can provide a complete function to a system and can be interchanged with other modules that provide similar functions. See also memory card, SIMM.