For all time; everlasting. But usually thought of a long period of time, and may be exaggerated from mere seconds to years.
Person 1:Dude! I haven't seen Bruno in forever!
Person 2: When did you last hear from him?
Person 1: Two days ago..
Person 2: Holy tits. If two days was a forever ago, I better change the dictionary.
"Those damn little kids, I swear. They say I'll love you forever on the first date, then break up the next week. It'll teach me to trust those little fuckers."