What do "Cup of Joe" mean?

The most popular explanation is that it was named for Admiral Josephus "Joe" Daniels (1862-1948), appointed Secretary of the Navy by President Woodrow Wilson. Admiral Daniels embarked on a series of reforms, such as the introduction of women into the service and effectively banning alcohol on board ships, including the officer's wine mess. This mainly left the sailors with coffee, which became referred to as Joe, after the Secretary.


Taken from http://www.IdiomIdiot.com/forum