Bit
The smallest unit of information — one choice between two alternatives, zero or one.
The word is a contraction of binary digit and is credited to the statistician John Tukey, who proposed it around 1946. Claude Shannon used it in "A Mathematical Theory of Communication" in 1948 and made it the foundation of information theory: a bit is exactly the amount of information needed to settle a fifty-fifty question.
Physically a bit is anything with two stable states — a voltage level, a magnetic orientation, a charged gate. Eight bits make a byte, which became standard with the IBM System/360 in 1964; before that, word length varied between machines.