Model based definition (MBD), also known as digital product definition (DPD), is the practice of using 3D digital data (such as solid models and associated metadata) within 3D CAD software to 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 use of 2D drawings to provide such details.
Use of the 3D digital data set 
Modern 3D CAD applications allow for the insertion of engineering information such as dimensions, GD&T, notes and other product details within the 3D digital data set for components and assemblies. MBD uses such capabilities to establish the 3D digital data set as the source of these specifications and design authority for the product. The 3D digital data set may contain enough information to manufacture and inspect product without the need for engineering drawings. Engineering drawings have traditionally contained such information.
In many instances, use of some information from 3D digital data set (e.g., the solid model) allows for rapid prototyping of product via various processes, such as 3D printing. A manufacturer may be able to feed 3D digital data directly to manufacturing devices such as CNC machines to manufacture final product.
In 2003, ASME published the ASME Y14.41-2003 Digital Product Definition Data Practices. The standard provides for the use of some MBD aspects, such as GD&T within the solid model. Other standards, such as ISO 1101:2004 and of AS9100 also make use of MBD.