In Aerodynamics or hydrodynamics The incidence is the angle that forms a profile with the fluid flow.

Depending on the shape profile of this incidence is measured according to clearly defined axis.

• For a flat plate immersed in a fluid, angle of incidence is the angle of its sides with the overall trajectory of the fluid.
• For a profile of wing , foil or Sail the incidencet of the profile is the angle formed by its proifile chord compared to the overall trajectory of the fluid.

The effect is a determining in calculating the drag and lift factor.