Dear Sirs

A DoE is a very specific type of multivariable experiment.  It is used to investigate various factors affecting your response variables.  It looks at the effects of input variables at two or more levels, and includes investigation into the interactions bewteen these variables.  There are very specific equations used to evaluate the results from these types of experiments.

You cannot call any experiment you decide to do a DoE, even if you are a really big important company.  Those are still just experiments.