The Jo is the Japanese short fighting staff; and Jodo is the WAY of the staff. It is descended from forms of Jo-jutsu (or jojitsu) which is the older, fighting version of this formal martial art.
The meaning of Way to the Japanese is like TAO to the Chinese… It’s a Way to self discipline, a Path to spiritual progress etc. Much more than just a martial art. So, if you like, Jodo is the Tao of Stick Fighting.
The five-foot Jo is nothing to be sneered at (even though it’s actually a few inches shorter than that). It is a fair match for a Japanese Samurai Sword, and in Ancient times it was not uncommon for Japanese policemen to disarm and arrest swordsmen using nothing but a wooden Jo.
Learning to use a Jo properly takes years of practise, and is normally done by students who are already advanced in other martial arts, such as Aikido or Kendo. (Notice, they are both Ways as well). The well-rounded martial artist would add Jodo to his skills as well.
Another art which is similar to Jodo is called Aiki-jo – and that is done by some Aikido students using a Jo as both an offensive and defensive weapon. For of course, just like a handgun, it can be either.