1) Lying in the same plane 2) Planar 3) Two-dimensional 1) Planar 
Co·plan'ar (ko*plān'ẽr) adjective [ Prefix co- + plane .] (Math.) Situated in one plane. 
[adj] - lying in the same plane
A set of points or lines that are all on a common plane. See also: Collinear.
adjective lying in the same plane
In geometry, describing lines or points that all lie in the same plane
being or operating in the same plane.