ASME Y14.100 : Engineering Drawing Practices
A document that describes essential technical requirements for material and the criteria for determining whether those requirements are met.
Alternate Definitions:

DAU - A document used in development and procurement that describes the technical requirements for items, materials, and services including the procedures by which it will be determined that the requirements have been met. Specifications may be unique to a specific program (program peculiar) or they may be common to several applications (general in nature).