GB/T 24630.1-2009 is the basic part of the flatness-related standards in the product geometric technical specifications. It systematically combs the professional vocabulary in the field of flatness, clearly defines terms such as flatness error and ideal plane, and avoids ambiguity in communication. At the same time, it specifies the key parameters used to describe flatness, including shape parameters, evaluation parameters, etc., and specifies its calculation method and value range. Provide a unified terminology system and quantitative basis for subsequent flatness measurement, evaluation and application in product design and manufacturing, and help various industries to accurately grasp the concept of flatness to ensure that product flatness accuracy meets standards.