Adjective
Between planes.
(aviation) Between the planes (wings) of a biplane or multiplane.
interplane strut
A small number of biplanes, such as the Zeppelin-Lindau D.I have no interplane struts and are referred to as being strutless. Source: Internet
Bays The space enclosed by a set of interplane struts is called a bay, hence a biplane or triplane with one set of such struts connecting the wings on each side of the aircraft is a single-bay biplane. Source: Internet