box number
noun[C]
COMMUNICATIONSukus(alsobox)anumberyou can give forpeopletocommunicatewith youinsteadofyouraddress,especiallyinadvertisements:
When thenewspaperinsertsa boxnumberin an ad andforwardsthereplies, theservicechargeis $75.
post office/postal/PO box numberHeaskedforchequesto besentto apostalboxnumber.