Parametric design is a design method where features (such as building elements and engineering components) are shaped according to algorithmic processes, in contrast to being designed directly. In this method, parameters and rules determine the relationship between design intent and design response. [from Wikipedia
Parametric Design refers to a process that sets up the shape and geometry of a design through parametric modeling
. To make it work, you set the geometrical parameters into a design tool that later uses computer processing to build relations between those parameters. The designer then uses multiple design variables to explore all the design possibilities.