Not just the USA. New Zealand calls it "de facto marriage" https://www.justice.govt.nz/family/separation-divorce/divide...

Isn’t it the same as a defector relationship? Australia also has a system where you don’t have to be married to be considered as a couple for some legal purposes.

You mean "de facto relationship"? From what I understand, no, it's the exact opposite.

https://www.gotocourt.com.au/family-law/de-facto-relationshi...

"The courts can make an order for the division of any property that you own together or separately. They may also order a split of any superannuation, or that one party pay spousal maintenance.

The net asset pool will include anything acquired before, during, or after separation. It does not matter whether the property was owned jointly or individually. When determining a property settlement, the court evaluates the types of contributions – financial and non-financial – made by either person, as well as their future needs."

Edit: this applies to AU "de facto relationship" vs UK "common law marriage" terms... it might be different when discussing different countries.

Indeed “defacto”. Damn auto correct.

>Is this just a US thing?

Canada too.