A cup of coffee. Though the true origin is unknown, "joe" as a synonym for coffee is theorized to either be a shortening of "jamoke" (a combination of Java and Mocha, two major suppliers of coffee beans), or as a reference to it being the drink of the ordinary man (i.e., the "average joe"). Primarily heard in US, South Africa. I can't even function in the morning until I've had my first cup of joe.