Can someone please explain...

What exactly comprises an island transfer? I have been seeing all kinds of OS sims and full prim sims that say that you can transfer them to an individual. I can understand an full prim sim able to do that but how is it able to be transferred for an OS/HS if a person does not own a full prim sim first. I know that tons of people are dumping their OS sims but is it possible to transfer ownership of one?

Thank you in advance!

You can only transfer an openspace/homestead sim to another resident who owns at least one regular sim. For a few months there was this weird thing where they let non-regular-sim-owners become the direct payers on an openspace if they had sponsorship from a regular sim owner. That is no longer allowed.

So yes, you can definitely transfer openspace sims to other residents (and you can transfer up to 4 at a time for a single $100 transfer fee), but only to people who own a full sim.

EDIT: You can ALSO transfer 4 openspaces to another resident who requests that they be converted to a single regular sim. That resident does not have to be a full-sim owner because they will be receiving a full sim, not an openspace.