ISO 42010: "An Architecture Viewpoint is a set of conventions for constructing, interpreting, using and analyzing one type of Architecture View. A viewpoint includes Model Kinds, viewpoint languages and notations, modeling methods and analytic techniques to frame a specific set of Concerns. Examples of viewpoints: operational, systems, technical, logical, deployment, process, information."1
IEEE 1471: A pattern or template from which to develop individual views by establishing the purposes and audience for a view and the techniques for its creation and analysis.