Decalage

Decalage on a fixed-wing aircraft is a measure of the relative incidences of wing surfaces.

[1] In a survey of representative biplanes, real-life design decalage is typically zero, with both wings having equal incidence.

In other fixed-wing aircraft, "decalage" typically refers to geometric decalage, which is the difference in the angle of the wing's chord line and the horizontal stabilizer's chord line.

The term "aerodynamic decalage" can refer to a similar angular measure that is taken with respect to each surface's respective zero-lift line rather than its chord line.

Aerodynamic decalage can be used to quickly assess the trim and stability of any two-surface airplane (e.g., a conventional or canard configuration, neglecting fuselage aerodynamics).