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Literally co-planar means acting on a same plane.
Coplanar force systems have all the forces acting in in one plane.
They may be concurrent, parallel, non-concurrent or non-parallel.
Co Planar classification :
Forces that act in a single plane; thus the forces are parallel to the plane and their points of application are in the plane.
Coplanar forces act in the same plane. Two balanced forces are equal in magnitude but opposite in direction to the other.