A combination of the words "stun" and "dong," it literally means stunning penis but in practice is more often used in place of the word strong. When used in place of strong, stong either implies an association with or jokingly refers to a stunning penis or implies male dominance in general. Stong is a form of sexual innuendo and can be used as a noun or adjective.
adjective use: "I have a stong pimp hand" implies male dominance whereas the phrase "I have a strong pimp hand" only implies superiority.
literal use: "He wants to show you all his stong."
sexual innuendo: "This statue looks stong" directing the listener to check out the statue's genitals.