It's the smallest piece ("bit") of information possible.
I seem to recall from long ago that a byte (lower case "b") was four bits, and eight bits was a Byte (with a capital "B"). (?)
Hey, we're talkin' 50 years ago, here. I took my first computing engine course in the early 60s. ... that's 1960s, not Babbage's 1860s.
Despite what you might be thinking.
Nowadays, with our penchant for acronymizing everything, it would have been called a SPOIP instead of a "bit."
As in, "That machine has a 64-SPOIP processor."
Terry, 230RN