User Parameters are unique variables that you can leverage to control or link your model in ways that aren’t available by default in OpenVSP. There are always 16 predefined user parameters that will always have the same Group, Name, and ParmID regardless of which model you are using. This makes them very robust in scripting and automation. Perhaps of greater interest to the designer is the ability to create custom parameters and adjust them from this menu. Once a user parameter has been created, the parameter is available for adjustment or linking as with any other model parameter. For example, a wing may be sized according to gross weight and wing loading rather than by span and area. An propeller may be sized according to the thrust, disk loading, tip speed, etc. So you can see how leveraging User Parameters in your model can enable a wider variety of parametric variation than would otherwise be available by default.
User Parameters may also be used to store numerical information in your model and not be linked to any other parameter at all. For example, you can create an integer type to keep track of the model version or use a double type value to record a target lift coefficient or maximum span. Be creative!