Answer:
perpendicular line through a point on a line
Explanation:
The circle centered at C seems intended to produce point D at the same distance as point B. That is, C is the midpoint of BD.
The circles centered at B and D with radius greater than BC seems intended to produce intersection points G and H. (It appears accidental that those points are also on circle C. As a rule, that would be difficult to do in one pass.)
So. points G and H are both equidistant from points B and D. A line between them will intersect point C at right angles to AB.
Segment GH is perpendicular to AB through point C (on AB).