Hot Pack (90s): A randomly inserted pack containing all inserts and no base cards. In the mid-90s, most Fleer sets came with one insert in a pack. But for 1995 Fleer and both series of 1995 Ultra, randomly inserted "Hot Packs" would yield nothing but inserts. About half the cards in a typical Hot Pack would be of the pack-specific insert with various other inserts making up the remainder. For example, a 1995 Fleer Baseball Hobby edition Hot Pack would contain six of the Hobby-only "Team Leader" inserts, with the other six being cards from the other various insert sets.
Fleer was not the only company in the mid-90s to use Hot Packs. 100 packs containing a full set of all 12 serial-numbered Donruss Elite inserts (all with matching serial numbers) were randomly seeded into boxes of 1995 Donruss Series Two.
Hot Pack (present day): An unopened pack of cards offered for sale, usually on eBay or other similar websites, that supposedly guarantees either an autograph or game-used insert.
Some products, like 2007 Ultra SE had a "hit" in every pack. However, most hot packs that are offered for sale over the internet are packs that have likely been examined by a pack searcher, and usually purchased at a mass-market retail outlet.
Of course, since there is no way of determining if an unopened pack has either an autograph or game-used card until it is actually opened, it is not advisable to purchase such packs.