A mood common among middle classteenagers, vibing is when you kick back, listen to some tunes (mainly slower rap and alt, but vaporwave, lo-fi, and others are becoming popular) and just relax. Some people vibe while stoned, some don't.
"Jesus, it's been 3 fucking hours, what the fuck is jessica doing?"
"Man, she's stoned af and vibing to some music. Let her be"