What does 'parametric' refer with regards to 3D modeling software?

If you are a candidate for a design role, then this question may be asked to gauge your familiarity with different types of Computer Aided Design (CAD) software. Parametric modeling is a popular type of modeling within the engineering world, and it describes software that defines geometry with a series of relationships (or parameters). It is similar to drawing shapes in Microsoft Powerpoint in that they can be changed at any point in the process, whereas direct modeling is more like drawing in Microsoft Paint. Once you lay down a layer, it is fixed and can only be erased or drawn over. Direct modeling is often more simple and intuitive in the earlier phases of design, but it can be more time consuming to modify as the design progresses.