Completing the squares we get:
36(x^2+4x+4)+4(y^2+12y+36)-288+144=0;
36(x+2)^2+4(y+6)^2=144;
Divide through by 144:
((x+2)^2)/4+((y+6)^2)/36=1, an ellipse.
Centre is at (-2,-6) and a=semimajor axis has length 2, b=semiminor axis has length 6, where:
((x+2)^2)/a^2+((y+6)^2)/b^2=1.