This language specification defines the Abbreviated Test Language for All Systems (ATLAS) . The term "all" was substituted for the original "avionics" in recognition of the wider application of the language. ATLAS is a standard abbreviated English language used in the preparation and documentation of test procedures which can be implemented either manually or with automatic or semi-automatic test equipment. This document amplifies the formal definition of ATLAS (Chapter 18) by providing functional description and rules applicable to ATLAS constructs over and above the syntactic definition of the language. To provide for a complete, but concise, description of each language construct a reference to the appropriate section(s) of the Formal Syntax of the ATLAS Language (from Chapter 18) together with a diagrammatic representation of the language syntax are included, where deemed appropriate, within this document. The diagrammatic representations are referred to as "syntax diagrams" and are intended to provide a guide in constructing valid ATLAS statements.