A giver of sperm, whether it be to your mother or yourself. The word daddy is often used by small children to refer to the poor bastard that has to take care of them, and is also used by teenagers to refer to someone they want to blow to the edge of the Milky Way.
daddy is a sexual term used by young females as a exclamation of appreciation for males, preferably to photos of guys that are absolutely hot as hell and they kinda want to smash.
Girl1: hey check out this photo Dominic justposted on his instagram!
Girl2: OMG daddy fr~