IDEF (Integrated Definition) represents a family of enterprise modeling languages used for modeling activities that support system analysis, design, and improvement. The document outlines various IDEF methods, including IDEF0 for function modeling, IDEF1 for information modeling, and IDEF1x for data modeling, detailing their purposes, strengths, and weaknesses. It also discusses the historical context of IDEF's development and its applications in enhancing communications and understanding within systems.