hmmm i think its where u have to dilute a substance by a suitable factor, why you would want to im not too sure, but one example i can think of from the top of maH Head is where you are doing a titration on ethanoic acid (vinegar)...so you would have to apply a suitable dilution factor before titraiton...
so say you wanted to dilute some 1M CH3COOH to a specified 0.1M CH3COOH, then you would have to apply a diluition factor of one in ten...
HOW? Well you get a measuring cylinder and add one unit of acid, to this add 9 mls of water and reconstitute....hope this helps