criteria that designers should meet in designing some system or device... so it really depends on what you are designing.
For example, when designing a chair, the criterais will include materials specified (wood, metal plastic) fasteners (bolts, welds), size (height, weight, depth) style ( curved, angular) weight( for shipping) size packaged ( as opposed to size assembled, think falt ikea boxes) etc etc etc...
So a design specification is really a list of what is needed to make the final design.
Same concept applies to fashion design, molecular, chemical etc... see what you want the final product to be, then break it down into its parts.
Hope that helps...
