1. The number of a letter box at the post office where mail is collected
   "Her business mail went to PO box number 2534"; "Her business mail went to post-office box number 2534";
   - post-office box number, PO box number, PO Box No
    
2. A mailing address to which answers to a newspaper ad can be sent
   "Responses to the job listing should be sent to Box Number 1234"

Derived forms: box numbers

Type of: mailing address