Short for "Regular Day Off". Often used when someone on salary either leaves early or takes a 'personal' or 'mental health day'.
Similar to skipping school, but for the blue collar worker.
"I'm going to RDO and go fishing on my boat. I can't deal with this (job) anymore."
Bill:Hey man you check out those new films at RDO?
Ted:Yea man they're the shit!