Concurrent forces are those forces whose lines of action meet at one point.
The forces, which meet at one point and their lines of action also lie on the same plane, are known as co-planar concurrent forces
The forces which do not meet at one point and their lines of action do not lie on the same plane are known as non-coplanar non-concurrent forces
Co-planar concurrent forces are those forces which meet at one point and their lines of action also lie on the same plane
Non-coplanar concurrent forces are those forces which meet at one point, but their lines of action do not lie on the same plane.