From WordNet (r) 3.0 (2006) :
open interval n 1: an interval that does not include its endpoints [syn: open interval, unbounded interval] [ant: bounded interval, closed interval]From The Free On-line Dictionary of Computing (30 December 2018) :
open intervalA type of interval (range of numbers) that does not include either of its endpoints. For example, when mixing red and blue paint, the proportion of red lies in the interval 0% to 100% but can't be exactly 0% or 100% or it wouldn't be a mixture. (2015-04-26)