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]

The Free On-line Dictionary of Computing (19 January 2023):

open interval

    An interval that excludes both endpoints.

   For example, a mixture of red and blue paint can contain
   between 0% and 100% red but 0% or 100% wouldn't be a mixture.

   (2015-04-26)