GB/T 24631.1-2009 is the basic part of straightness specification. It systematically organizes professional vocabulary related to straightness, clearly defines key terms such as straightness error, ideal straight line, etc., and eliminates understanding deviation in industry communication. At the same time, it clearly describes various parameters of straightness, including shape parameters, tolerance parameters, etc., and specifies its value range and calculation method. This builds a unified terminology system and quantitative standards for the measurement, evaluation and application of straightness in product design and manufacturing, helping various industries to accurately grasp the concept of straightness and ensure product mass.