Coplanar forces are forces on a single plane. This means that all points of application are inside that plane and that all forces are running parallel to that plane.
Coplanar forces may be concurrent, non-concurrent, parallel or non-parallel. A concurrent force includes at least two forces where all lines of action come together at a common point. A non-parallel and non-concurrent force has vectors that are not parallel and not meeting at a single point. These are the hardest forces to resolve because they are a jumble of forces. A parallel force includes at least two forces where all lines of action are parallel.