The meaning varies with context, but it's essentially "Let go".
Similar to 60s let it all hang out, but with lots more excitement.
Turn loose, go wild, get crazy!
Remember "leggo my eggo"? Still let go. Different connotation, though.
I hope it annoys you that a 60 year old fart such as myself knows more about current slang that you do, simply because my google-fu is strong. Perhaps you should get your twinkly little fingers off their butts and use them to answer your own questions.