Note that I'm not talking about "visiting professor" or "visiting lecturer" positions in the US, which seem to be full-time non-tenure-track positions offered at some US universities.
What I mean is that I sometimes see people list "visiting researcher", "visiting scholar", or "visiting professor" as their second affiliation, and seemingly they are not actually being paid by the second institution (their full-time position is at their primary place of employment) but they simply maintain a second affiliation through this visiting position. Often I see people having visiting affiliations at universities in other countries, or professors keeping a visiting position at their previous place of employment after they moved to another place.
What are these visiting positions? How does one get it, and what is the point?