Packs are specific groupings of tickets.
Typically used with the number of tickets within a grouping preceding the word "pack." For example, a seller may say they have a replacement offer for a 4-pack. In this example, the "4-pack" refers to a group of 4 tickets together.
Packs are similar to "splits" in that both refer to a grouping of tickets. However, a pack is more commonly used to describe a general group of tickets, whereas splits refer to the minimum amount of tickets that a pack can be split up into.