A Table Pack is a set of tables based on a common theme. For example, there's the Science Fiction Table Pack, which contains about 30 tables useful in running SF-themed games. One of those tables produces ideas for possible adventures, another does headlines for a future newspaper, and so on. Table Packs include Fantasy I, II, and III, Science Fiction, Apocalypse, and another one that I'm not announcing the theme of until it's close to release.
Table Packs are great for the GM who doesn't have the time to write up a lot of tables and just wants to customize existing ones, or who needs something to start with and then can fun with it. Since you can change and modify a table any way you want, the genres are not fixed in stone. Many tables can be used, with little or no modification, in several different genres.