Model-Based Testing (MBT) is a technique where a visual model is used to drive our testing.
A model is simplified representation of relationship, process, or a system (please read a quick overview on MBT here).
Models can be built around flows, transition of pages, internal states, calculations, etc; there are many different ways of modeling and in itself is a challenge and an art.
MBT can be combined with automation to provide greater coverage and explore the system dynamicaly, until a certain criteria (e.g. time, edge coverage) is met.