# Boundaries

All fluid networks have start and end points. These "points" are called boundaries within the concept of FluidFlow. Boundaries are therefore the points where the model starts and terminates. Correct selection of model start and end boundaries is a simple skill you should know in order to build your model. FluidFlow has many types of boundaries available. Generally at a network boundary you will either know (or have as a design goal) either the pressure or the flowrate.