off-by-one error

(Or "Obi-Wan error") An exceedingly common error induced in many ways, such as by starting at zero when you should have started at one or vice-versa, or by writing "< N" instead of "<= N" or vice-versa. Often confounded with fencepost error, which is properly a particular subtype of it.

The term zeroth corrects the linguistic off-by-one error of, e.g., referring to the "1st" element of an array whose indexes start from zero.

[Jargon File]