What is interstice? interstice is gapWhat is gap? Petit espace vide entre les parties d'un tout : Boucher les interstices des volets.Small space empty between the parts of a whole: fill the interstices of the shutters.Partie, de dimension le plus souvent microscopique, comprise entre les cristaux d'une roche.Part of dimension often microscopic, between the crystals of a rock.