My understanding is that there's a waiver deadline at the end of August, and it means that players involved in trades have to clear waivers before the trade can go through. So every MLB team has a chance to essentially block the trade, which is why big time players usually don't get traded after the non-waiver deadline. Speaking of which...
The non-waiver trade deadline (which passed last week) is for traditional player(s) for player(s) trades.
I don't know why exactly they've made that distinction, but that's the way it is.
