Model-based definition (MBD), sometimes digital product definition (DPD), is the practice of using 3D models (such as solid models, 3D PMI, and associated metadata) within 3D CAD software to define (provide specifications for) individual components and product assemblies. The types of information included are geometric dimensioning and tolerancing (GD&T), component level materials, assembly level bills of materials, engineering configurations, design intent, etc.

By contrast, other methodologies have historically required accompanying the use of 2D engineering drawings to provide such details.