In the context of GIS and geoprocessing, is a visual programming language used to create, edit, and manage geoprocessing workflows. It allows users to automate complex tasks by stringing together a sequence of tools where the output of one tool becomes the input for the next.
These tutorials provide a practical look at building and streamlining workflows using ModelBuilder: Getting Started with Model Builder in ArcGIS Pro YouTube · ArcGIS Introduction to ArcGIS Model Builder YouTube · GeoDelta Labs ArcGIS Pro Tutorial: Model Builder YouTube · Ken Yanow Model Builder