high bit n.

[from `high-order bit'] 1. The most significant bit in a byte. 2. [common] By extension, the most significant part of something other than a data byte: "Spare me the whole saga, just give me the high bit." See also meta bit, hobbit, dread high-bit disease, and compare the mainstream slang `bottom line'.

--The Jargon File version 4.3.1, ed. ESR, autonoded by rescdsk.