USPS Tracking shows my package was delivered to a Parcel Locker. What does that mean?

In some circumstances, a package being carried by USPS may be delivered to a Parcel Locker. A key or other form of notification should be left in the recipient’s regular mail receptacle indicating the package is in a parcel locker. If you need help locating your nearest parcel locker, please contact the facilities manager at your property or your local Post Office for additional instructions.

Some helpful resources with information regarding parcel lockers are: https://faq.usps.com/s/article/What-is-a-Cluster-Box and https://www.mailboxes.com/salsbury-mailbox-blog/what-is-a-parcel-locker/.