higher-order bit
The salient point of a document, conversation, etc., that accurately summarizes it. Originated in Computer Science circles, from binary numbers, where the highest-order bit is worth more, numerically, than the rest of the bits put together.
Sue: I can't believe what an awful time I had with Rob! First we had to wait, like, FIVE minutes for a table, even though we had a reservation! Then we were sitting next to these people who were like so strange looking. Then I told him all my problems and he just got bored.
Jim: I think the higher-order bit here is that you're a bitch.
Jim: I think the higher-order bit here is that you're a bitch.