Literally means, must be off.
Usually used in any employee scheduling that is not typical 9a-5p but with work that varies with hours and days.
It means that no matter what this employee will not be available under any circumstances.
John has an MBO next Monday because he's having oral surgery.
Texting abbreviation for Mind Blowing Orgasm. 'Nuff said!!
Omg I just had multiple MBOs with my Husband!!!