The second definition of the squircle was given by Fernandez Guasti (1992), but apparently not dubbed with the name "squircle" until later (Fernández Guasti
et al. 2005). This curve has quartic Cartesian equation

(6)

with squareness parameter ,
where corresponds to a circle with radius
and to a square of side length . This curve is actually semialgebraic, as it must be restricted
to to exclude other branches.
This squircle encloses area

Fernandez Guasti, M. "Analytic Geometry of Some Rectilinear Figures." Int. J. Educ. Sci. Technol.23, 895-901, 1992.Fernández
Guasti, M.; Meléndez Cobarrubias, A.; Renero Carrillo, F. J.; and Cornejo
Rodríguez, A. "LCD Pixel Shape and Far-Field Diffraction Patterns."
Optik116, 265-269, 2005. Sloane, N. J. A. Sequence A186642
in "The On-Line Encyclopedia of Integer Sequences."