ORIGINAL: TFF
It is the Cord line, and with reference to the centerline of the fuselage, the angle measurement makes the angle of incidence.
You are right in that it is the cord but not in that the angle it makes with the fuse is angle of incidence. The angle of incidence is the angle between the chord of the stab and the cord of the wing and can theoretically be at any angle to the fuselage center line.