What does a green card professor mean?

A green card is a proof that a foreigner has the right to detention in another country. Generally, the green card is always valid in this country, which means that you can live indefinitely in the country where the green card is issued without applying for any visa. However, if you don't live in the local area and go to other countries after getting a green card, your green card will expire in a few years. For example, in Australia and Canada, you can only renew your green card if you live in your country for 2-3 years every five years. If you don't have enough time and people are abroad, the green card will be invalidated directly, so everyone calls this policy immigration supervision, that is, you should leave enough time even if you don't want to live, otherwise the hard-earned green card will be gone. It seems that only New Zealand has a permanent green card in the immigrant country, and you can get a permanent green card as long as you live for half a year every two years after you get it. This green card can live outside New Zealand indefinitely and will not expire.