[djohn]

It really depends on the set. However I generally consider it the base set with all SPs and variations. I don't consider inserts and parallels part of a master set. That being said, I still end up putting together most of the easy insert sets when doing a master set.
I have been working on a complete MASTER set of 2001 Upper Deck Prospect Premieres including ALL the inserts. I have finished the base set with autos, all the single and double game used cards, and am 1 short on the triple game used (the Mantle/DiMaggio/Maris SP). I finished the Jackie Robinson game used set and gold parallel set (#'d to 42), however I still need the 3 autographed versions. I also have 4 of the 5 Michael Jordan bat cards (only missing the MJ5 shortprint). The only portion of the set I haven't started are the 22 game used autographs as they are only 25 of each made and they tend to be fairly expensive when they do come up for sale.
When it comes to Master Set building it really just comes down to how much money you want to spend.