At this point, we have not actually received the product yet. This is just showing us the details on the product that we are ready to receive. The WH/IN/00001 is sequentially assigned for each transaction.
Please be aware that it is possible the transaction name WH/IN/000001 may be different in your installation, as Odoo changes the sequences that are defined in a default installation from time to time. These names can be user-configured by going to Settings | Sequences & Identifiers | Sequences. You could even change the default prefix from PO to whatever you desire, as long as it does not conflict with the prefix of another module.
The WH in the name is short for warehouse and the IN is short for incoming goods. When we are receiving products into inventory, we are creating an inventory transaction. You can see the associated purchase order under the Source Document field on the right side of the form. We can also see the actual time the order was received compared to the scheduled time of the order. In this case, we can see we received the order in plenty of time.