Off-by-one Error

/ȯf-bī-wən er-ər/
n. Exceedingly common error induced in many ways, such as by starting at 0 when you should have started at 1 or vice versa, or by writing '< N' instead of '<= N' or vice-versa. Also applied to giving something to the person next to the one who should have gotten it. Often confounded with fencepost error, which is properly a particular subtype of it.