(education) The distinction drawn by some language teachers between an "error" (a mistaken belief that a given usage or construction is correct; or, an incorrect use resulting from such a belief) and "a mistake" (an accidental use of a usage or construction despite knowing that it is incorrect).

(numerical analysis) The difference between the result produced by a given algorithm using exact arithmetic and the result produced by the same algorithm using finite-precision, rounded arithmetic.

(computing) An error that occurs when an operating system halts, because it has reached a condition where it can no longer operate safely.

(programming) A logic error where a value, typically the number of iterations of a loop, is specified incorrectly, being either 1 less or 1 more than it should be.

To understand the reasons for which one's prior conduct was wrong or mistaken.

(uncommon) Characterised or marked by error(s).