What is the difference between a plexus and a ganglion?

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.