a parabola
The shape described by the intersection of the cone and the plane is simply a circle.
The intersection of a right circular cone and a plane that is parallel to the edge of the cone is a parabola. However, if the vertex of the cone lies on the plane, then the intersection is simply two intersecting lines.
A parabola is the figure formed by the intersection of a circular cone and a plane that lies parallel to the edge of the cone. (the cone does not have to be a right [90°] circular cone).
It is a circle - or at its extreme, a point.
The intersection of the cone and that particular plane is a parabola.
Then the intersection is a hyperbola.
I'm assuming you are looking for the name of the conic section produced by this type of intersection? If a right circular cone is intersected by a plane parallel to one edge of the cone, the resulting curve of intersection would be a parabola. If the intersecting plane was parallel to the base, it would be a circle. If the intersecting plane was at any angle between being parallel to the base and being parallel to an edge, it would produce an ellipse or part of an ellipse (depending on whether the intersection was completely within the cone).
If a right circular cone intersects a plane that runs parallel to the edge of the cone the result curve will be a parabola, unless the intersection includes the vertex of the cone, in which case the intersection is a straight line. This is a conic section. Depending on the angle of the plane, the section will be a circle, an ellipse, a parabola, or two hyperboles.
The hyperbola is the curve at the boundary of the intersection of the conewith a cutting plane parallel to the cone's axis.
Conics, or conic sections, are the intersection of a plane with an infinite double cone. If that plane cuts both cones, it is a hyperbola. If it is parallel to the edge of the cone, you get a parabola. If neither is the case, it is an ellipse. The ellipse is also a circle if the plane is perpendicular to the altitude of the cone. Note that none of these are the case if the plane passes through the vertex of the cone.
The interception of a plane with a cone parallel to the base of the cone is a circle.
The points where the cone and plane intersect will form a circle.