An Artifact is any physical piece of information used or produced by a system, represented in a Deployment Diagram. Artifacts can have associated properties or operations, and can be instantiated or associated with other Artifacts. Examples of Artifacts include model files, source files, database tables, development deliverables or support documents.
OMG UML Specification
The OMG UML specification (UML Superstructure Specification, v2.0, p. 185) states:
"An Artifact defined by the user represents a concrete element in the physical world. A particular instance (or 'copy') of an artifact is deployed to a node instance. Artifacts may have composition associations to other artifacts that are nested within it. For instance, a deployment descriptor artifact for a component may be contained within the artifact that implements that component. In that way, the component and its descriptor are deployed to a node instance as one artifact instance."