Why do people have masters or pets on here? Im not so sure i get it.

I see that  sevlowtyak has 3 masters, and he has called other furs pets, but are they really his pets in real life? or are they just pets online?

and i saw that  super-fluffy has a pet too, i think he is one that Sev calls pet as well, so do pets belong to both partners in a mateship here? I dont understand it fully.

can someone explain it to me?