Factory set: A complete set, put together by the manufacturer, and sold in a special package. Topps has made these since the 1970s, and other makers have put them out from time to time, but some can be tough to find. Most of the time, the value of these sets is comparable to hand-collated sets, but scarcity can drive the price up, such as with the 1997 Topps baseball factory set. One important note is that factory sets must remain sealed to keep any premium value that they might have over hand-collated. Kind of dumb, but true. The idea is that sealed factory sets are possibly filled with Gem Mint cards. Opened factory sets do not hold that mystery.
Topps actually made factory sets as early as 1962 or so, but they were called "Presentation Sets" and they weren't available to the general public. Mainly they were salesman samples, promotional items or given away to a few people as gifts. Cards from these sets are often advertised as such, and usually they are in better condition than most other cards, as they haven't been handled as much or gone through the wax pack process.