In World of Warcraft, it means that an item is ungivable to anyone else. Quest rewards and phat l00t are nearly always bind on pickup, meaning that the only way to get rid of them is to sell them.

Internet persona(s) who happens to follow you and you happen to follow them back and maintain communication with and have a mutual liking for eachother whether it be friendship wise, etc. (Mutuals if more than one mutual)

When an item like Krol Blade becomes attuned to your very soul. The weapon then only accepts you as its true user because like a chick, it gets very clingy.