English pet name for Joseph, from Hebrew "Jehovah gives children", sometimes used as a given name in its own right.  The spelling variant Jo is usually but not exclusively, female.

While Joe is universally understood to be a diminutive or pet name for Joseph, one correspondent [LA] wrote:

      "I had a Great Uncle known to family as Joe. After a great deal of searching for Joseph, I was able to locate his family and found that his name was actually George. The family used the abbreviation Geo. which, when spoken, is pronounced 'Joe'."

Although the above anecdote is from Oregon, USA, it is quite possible that some records of "Joe" in English-speaking countries, especially in Census records, should more properly have been "Geo.", the standard abbreviation for George.