Agile modeling is an approach to the modeling aspects of software development. It’s a practice for modeling and documentation for software systems. In one line:
It’s a collection of best practices for software modeling in a lightweight manner.
In abstraction, we can say it augments other software processes. For instance, let’s say your company is using UML and then Agile applies approach practices on UML. For example, “Keep things simple” is an Agile approach. So it means that we do not need to use all the diagrams in our project, use only those which are needed. If we summarize, we can say Agile modeling says “Do only what’s needed and nothing more”.
Figure: Agile modeling