A geometric model is a probability model in which the probability of each outcome of an experiment is associated with a region in a geometric shape. The associated region in the shape is proportional to the probability of the outcome. A common example of a geometric model is associating all the outcomes of an experiment to regions on a spinner.
Looking at the spinner, there are several regions of different sizes. Each region is associated with an event such that events with a greater probability of occurring are associated to a larger region in the spinner.