Toughie this one - as unfortunately some accomodation suppliers don't quite understand the meaning, and therefore can give misleading descriptions.
The dictionary describes it as "adapting to the climate or environment". Which means to me, that as it gets warmer outside... so the pool would increase in temperature. Likewise... if the air temperature drops, then the pool will follow. (actually we could have a whole conversation here about how water, air and earth all change temperature at different rates yada yada... but we'd be here til Easter)
I think it means "only jump in if you're really brave between October and March, because it'll freeze bits off you that you didn't know you had! But for the rest of the year, it's a welcome relief from the heat"
But that's just my personal opinion. I have an acclimatised pool, and haven't been in it very much lately... but some would say that's because I'm a Southern Jessie.
A large number of people relish the cooler pool - and that's great too. I used to see the old fellas out swimming on New Years day in Portsmouth. And I think our Celtygirl here quite likes her Northern Waters (but then she's kept warm with Irn Bru... and is a nutter)
This subject was broached previously, and caused lots of discussion.
Have a read - and I hope that it helps you make your mind up. If you can let us know which villa it is, that you are looking at - then maybe someone could go dip a toe for you
Good luck hon!