The locus of points oscillating in phase constitutes a wavefront. When a point light source is positioned at the focal point of a convex lens, the emanating light rays are rendered parallel. These parallel rays generate a plane wavefront, where all points are equidistant from the source and travel in the same direction. The convex lens, through its focusing capability, converts the initial spherical wavefront into a plane wavefront. Final Answer:\[\boxed{\text{Plane}}\]