A realm of experience is any formally contiguous phenomenological subset of reality. In the most usual setting, a realm is a parallel reality with arbitrarily different physics. In the Faery realm, for example, time is oft said to flow "without measure," meaning that time there does not flow with the same pace or linearity as our own. Less often, a realm refers to a parallel timeline with a formally distinct government.
Whenever two realities meet, the identity realm or realm of fiction is said to remain the same, with the settings considered fictional from the two merging cultures remaining fictional. There is no known evidence of a realm discovering another independent realm containing vast sections of real-world instances of settings considered fictional in the discovering realm unless the discovered realm had already been known to be created from the original realm through fiction manipulation. A primitive reality is any realm that has no evidence of contact with any other reality, and therefore has no preexisting methodology for readily describing boundaries between them.
Paranormal research initiatives such as para.wiki or /x/ have thus far not been successful in establishing evidence of contact with other realities, though interpretation to that effect is very common on the latter.