The concept of Parametric products is similar to the concept of Product Library.
In Product Library the parts in the product had fixed dimensions. Like the top of the table 1 Mt wide and 2 Mt long. But consider a case where you have to make many similar products just varying in the dimension.
Look at the two figures below, the two figures A and B are similar. Suppose you are making many similar cupboards of same design but of different sizes as shown below. If you use the ordinary product library then you will have to input them as two products.
But notice that, the dimensions of the parts are dependent on the Height, width and depth of the cupboard. For example the width of the left door of cupboard A and B is half the width of the cupboard. It means the dimensions of the parts are related with dimensions of the cupboard by a mathematical formula.
So if we input only dimensions of the cupboard, and the formula for the sizes of the different parts, we can automatically calculate the dimensions of the individual parts by giving the dimensions of the cupboard. This can be very useful while defining products and than inserting the BOM (Bill of Materials for the product) into PLUS 2D for optimization.