A ganglion is a soft tissue herniation, usually in a tendon sheath or joint capsule in which the soft tissues form a mass outside the tendon or joint. The enlargement is usually full of synovial fluid. Ancient myth is that you can hit the ganglion with a big book, traditionally a Bible then the enlargement can be forced back into the tendon sheath or joint capsule. It does not work very well and more conventional methods of treatment are usually needed.
Famous Words of Inspiration...
"Half of maturity consists of knowing when and how to be immature."