Parallelogram of Forces
A method of resolving two forces acting on an object. This is also a great way of visualising the forces and hence resultant.
OA and OB represent the magnitude and direction of two forces acting on point O
The diagonal OC of the parallelogram OACB represents the magnitude and direction of the resultant force.
This also works the other way around if the force is represented in magnitude and direction by OC then OA and OB represent the components of the force represented by OC.