The "trefoil" curve is the name given by Cundy and Rollett (1989, p. 72) to the quartic plane curve given by the equation
(1)

As such, it is a simply a modification of Kepler's folium with and
(2)

obtained by dropping the coefficients 2.
The area enclosed by the trefoil curve is
(3)

the geometric centroid of the enclosed region is
(4)
 
(5)

and the area moment of inertia elements by
(6)
 
(7)
 
(8)

(E. Weisstein, Feb 3, 2018).