It usually means the delivery guy didn't find the recipient home when he went to deliver the package to the address. Some express carriers like UPS will try again on the next weekday, they will make up to three attempts to pick up your package.
You have a few options here :
1. Call the recipient and tell him/her to pick up the package him/herself from the post office.
2. Contact the express carriers, and ask them to redeliver your package.