An interface defines the interaction between certain modules.

Interface is a very general concept which refers to the interaction points of arbitrary modules:

• The interface of a class is defined by its public methods.
• The interface of a method is defined by its method signature.
• The interface of a subsystem is defined by the public (facade) classes.
• The interface of a network service is defined by a protocol.
• The interface of a hardware component is defined by pins, wires, signals, protocols, etc.
• A graphical user interface is defined by buttons, menus, text boxes, and other controls.

The interface defines how a module shall be used. There may be ways circumventing the interface and accessing internal parts of a module directly. This should be avoided (IH/E but is sometimes done.

A module can be described as having a provided interface and a required interface.

• Module
• Application Programming Interface (API)
• Application Binary Interface (ABI)
• Service Provider Interface (SPI)

• Interface (computing)

An interface is a language construct of certain object-oriented programming languages resembling an abstract class without any implementation.

Note that in this wiki whenever the language construct is meant (and not the concept) interface shall be written using a monospace font: interface vs. interface.

• Class
• Abstract Class
• Mixin