What does the "PR" on the visa mean?

Permanent resident? permanent resident

Pr refers not to a passport, but to the nature of a visa, which means that you have no nationality but permanent residency.

Visa refers to the procedure of endorsement and seal of passports or other travel documents held by domestic or foreign citizens by the sovereign organs of a country to show that they are allowed to enter, exit or transit. It can also be said that it is an endorsement certificate issued to them. Generally speaking, a visa is a document issued by a country's entry-exit administration (such as immigration bureau or its embassy or consulate abroad) to approve the entry of foreign citizens.