In humans a nerve plexus is network of intersection nerves. Essentially nerves in the spine whose destination is the same are grouped into one large nerve (like many lanes on a highway instead of several isolated roads). There are six of these plexuses in the body: cervical (head, neck, and shoulders), brachial (chest, shoulders, arms, and hands), lumbar (back, abdomen goring, thighs, knees, and calves), sacral (pelvis, buttocks, genitals, thighs, calves, and feet), solar (internal organs), and coccygeal (internal organs).
A ganglion is a mass of nerve cell bodies. A plexus is made up of ganglia. They are essentially the relay points of the entire nerve.
Plexus, in anatomy, is a network of intertwining parts such as nerve fibres, blood vessels or lymphatics. For example, solar plexus is a network of nerves in the back of the stomach. Ganglion are a particular type of plexus that consist of a group of nerve cells forming a nerve center specially outside of the brain or spinal chord. Thus plexus is a general name of a bigger group of parts in human body, while ganglion is a smaller group within the larger group. Also while a plexus may consist of nerves, blood vessels or lymphatics, a Ganglion consists only of nerves.