1. Finished with one's work for the day. Often followed by the word "work." I'll be off at 6, if you want to meet me then. I need to get these presents wrapped before my wife gets off work.
2. Not attending work or school. I can't wait to be off on my vacation next month. I'm off for two weeks for Christmas, so we'll definitely hang out then!
3. Not correct or accurate. Often followed by "on (something)." The measurements were a bit off, so the shelves don't fit quite right. Sorry, your guess was way off! They were off on their initial valuation by several hundred thousand dollars.
4. Having begun something. Often followed by "on (something)." Dad's off on another mission to protect us innocent kids from violence in the media. I heard you're travelling to India—when are you heading off?
5. Travelling (to some place). We're off to the Bahamas for the next two weeks! I heard you're travelling to India—when are you heading off?
6. verb To kill someone, especially as a means of silencing or disposing of them. In this usage, the term is usually followed by a noun or pronoun. The gang offed the accountant before he could use his knowledge as leverage with the district attorney. I puked my guts out the first time I offed somebody, now it feels like second nature.
off on someone or something
in a rage about someone or something; on a tirade about someone or something. Are you off on Sally again? Why can't you leave her alone?