Lately, we've been getting a lot of immigrants from IMVU, Sony's virtual world. There, the world consists of "rooms", which may be public or private...and may not look like a room at all, but more like a bit of the outdoors.
People from IMVU are coming to SL, thinking that our world works the same way...and this can result in them making costly mistakes. Yesterday, someone posted on the SL forums that she'd bought a "room" and wanted to know "how to make it public so my friends can come to it".
What she had bought was a HOUSE...a rather large mansion, in fact. What she didn't realize was that she would also need land to put the house on...a rather large and expensive piece of land, too...at least 1/8 region.
IMVU players, listen up! Second Life has no "rooms". It has "regions", also called "simulators" or "sims" for short. The regions are the grid squares that you see on the main Map. Regions are generally open to the public, unless the region owner takes special steps to achieve more or less privacy. Most regions are subdivided into smaller parcels, which are owned or rented by residents for their homes and businesses.
While we do teleport from region to region, much as you went from room to room in IMVU, if regions share a border, you can also simply walk from one to the next, just like walking from one county to the next in Real Life.
Get those "rooms" out of your head, and welcome to the somewhat more realistic world of Second Life.