A plexus is like an electrical junction box in a house. In a plexus, nerve fibers from different spinal nerves are sorted and recombined, so that all fibers going to a specific body part are put together in one nerve.
Four nerve plexuses are located in the trunk of the body:
Because the lumbar and sacral plexuses are interconnected, they are sometimes referred to as the lumbosacral plexus.
The spinal nerves in the chest do not join a plexus. They are the intercostal nerves, which are located between the ribs.