1. [techspeak] The unit of information; the amount of information obtained by asking a yes-or-no question for which the two outcomes are equally probable. 2. [techspeak] A computational quantity that can take on one of two values, such as true and false or 0 and 1. 3. A mental flag: a reminder that something should be done eventually. "I have a bit set for you." (I haven't seen you for a while, and I'm supposed to tell or ask you something.) 4. More generally, a (possibly incorrect) mental state of belief. "I have a bit set that says that you were the last guy to hack on EMACS." (Meaning "I think you were the last guy to hack on EMACS, and what I am about to say is predicated on this, so please stop me if this isn't true.")"I just need one bit from you" is a polite way of indicating that you intend only a short interruption for a question that can presumably be answered yes or no.
A bit is said to be `set' if its value is true or 1, and `reset' or `clear' if its value is false or 0. One speaks of setting and clearing bits. To toggle or `invert' a bit is to change it, either from 0 to 1 or from 1 to 0. See also flag, trit, mode bit.
The term `bit' first appeared in print in the computer-science sense in 1949, and seems to have been coined by early computer scientist John Tukey. Tukey records that it evolved over a lunch table as a handier alternative to `bigit' or `binit'.