Answer
circle
Work Step by Step
The general equation of a conic in the form of $Ax^2+Bxy+Cy^2+Dx+Ey+F=0$ if $B=0$
(i) defines a parabola if $AC=0$
(ii) defines an ellipse if $AC\gt0$ and $A\ne C$
(iii) defines an a circle if $AC\gt0$ and $A=C$
(iv) defines a hyperbola if $AC\lt0$
Here $A=1,C=1$, hence $AC=1\gt0$, $A= C$, thus it is a circle.
