I’m not sure. Since it is related to the distinction in mathematics between open and closed intervals (except on computers we have floats in instead of reals),

I’m not sure. Since it is related to the distinction in mathematics between open and closed intervals (except on computers we have floats in instead of reals), maybe “interval error” or “endpoint error”. But not “bounds error”, of course. EDIT: Or maybe “comparison error”. I like that the best. But calling it an off-by-one seems wrong, especially as what we usually mean by that is something more like not handling the last iteration of a loop correctly.