An aëroplane with two main supporting surfaces one above the other.
Having, or consisting of, two superposed planes, aërocurves, or the like; of or pertaining to a biplane; as, a biplane rudder.
An airplane with two sets of wings, one on top of the other. Historically the biplane configuration was used as it improves the bending stiffness of the wing that was otherwise difficult to achieve in early monoplane designs. Search for biplane books on Amazon.co.uk