An interaction is defined as a unit of behaviour performed as a collaboration between two or more roles.

An interaction is similar to a process or function, but while a process/function may be performed by a single role, an interaction is performed by multiple roles in collaboration.

An interaction may be triggered by, or trigger, any other behaviour element (event, business process, function, or interaction).

An interaction may access passive structure elements.

An interaction may realize one or more services and may use (internal/same layer) services or services from "lower layers".

A collaboration may be assigned to a interaction.

The name of a interaction should preferably be a verb in the simple present tense.

Category: Layer and Behaviour aspect

Examples: Formalize Request, Check and Sign Contract, Take out Combined Insurance.

Typical Relationships:

Assignment - collaboration, application collaboration
Access - object
Triggering - event, process, function, interaction
Realisation - service

Source: A generalization of concepts defined at various layers in Archimate.