Packet swap was a college quizbowl procedure in which tournaments increase the number of packets blind to participating teams by exchanging with a tournament run on a similar date in a different region. A packet swap was differentiated from a mirror by the presence of packets originally submitted by teams participating in the tournament.
Due to the gradual replacement of "central editing packet swap" with unified editing teams who collaborate on one set across multiple schools, and the overall decrease in packet-submission college sets, it's now basically unheard-of for two different packet-submission sets to run on the same weekend, and packet swaps have largely been replaced outright by mirrors as a form of organizing the circuit.
There were two main types of packet swap: the direct packet swap and the central editing packet swap.
Direct Packet Swap
In a direct packet swap, tournament sites edit their packets independently, then exchange edited packets. Direct packet swaps are largely disappearing because the central editing method produces fewer repeats, fewer avoidable variations in difficulty, and less work for everyone involved.
Central Editing Packet Swap
In a central editing packet swap, tournaments receive unedited packets from participating teams, then exchange these raw materials between the tournament editors with a chief editor at one of the sites responsible for overseeing all sites' editing and the final packet assembly. Typically, this results in several tournaments contributing various subject editors to the overall finished product. ACF tournaments employ a variant of the central editing method in which the editing team does not necessarily come from the tournament hosts. Centrally-edited packet-submission sets with editors at multiple host sites are generally no longer referred to as "packet swaps" either, making the term basically useless.