A Frisian eagle is a specific heraldic eagle in a coat of arms.
It is a half of a black double-headed eagle in the golden half of the shield parted per pale, most commonly on the dexter side. In other words, it is a double eagle which has been subject to dimidiation.
The correct blazon in Dutch is: Gedeeld: I in goud een zwarte Friese adelaar komende uit de deellijn [Per pale: Or, a Frisian eagle sable rising from the line of partition].
It appears in many coats of arms from the area of the old Frisia.