(UK, informal) A fundamental, simple mistake.

plural of schoolboy error

A blunder that occurs as the result of a strenuous effort to avoid it, such as spilling a drink because one is concentrating on not doing so.

plural of ironic error

plural of error function

(idiomatic) A set of amusing or farcical events involving a series of awkward missteps or other mistakes.

(sports, especially tennis) An error caused by an opponent's good play

alternative form of errorfree

In the habit of making errors.

(computer graphics) A form of halftoning in which the quantization residual is distributed to neighbouring pixels that have not yet been processed.