In the previous system, what defines how a trade posts lives scattered: one table for operation types, another for rules, a formula file, a couple of includes. To know what a purchase does you have to open all five.
A pack brings all of it into one object: its ten balance-key dimensions, its eight cumulative settlement horizons, its measures — such as weighted average cost —, its amount formulas and its rules. It is versioned, approved and loaded; several packs coexist in the same tenant, each with its own book.
The practical consequence is that a new market is a new pack, not a new engine. And that the question “why was this entry generated?” has an answer you can read without opening the code.