Given curves C1 and C2 and a fixed point O. Draw lines l through O that intersect C1 in Q1, and C2 in Q2. Then the cissoid is defined as the collection of points P (on l) for which OP is equal to the distance between the intersections (Q1Q2). Some special cases of the cissoid:
The first cissoid to be discovered was the cissoid of Diocles.