By "casas", the reference is to licensed "casas particulares", which can be a room (or rooms) in someone's house/apartment, a room (or rooms) with a separate entrance within the residential structure, or a separate apartment or house. There are also hotels, most of which seem much more expensive.
casas particulares - literally "private houses" but normally referring to private houses licenced to rent rooms to visitors.
When are you planning to visit ?

Last week in January which is our coldest time here in Minnesota. Thank youfor your help. I'll check out cubajunky.com any other recommwndations for booking?

Thank you for your response! We're looking for 1 week, Havana for a few days and beach area close to Havana-looking at Verdara but looks touristy. -any less touristy beach area close to Havana you'd recommend? Thank you in advance. Any issues w/proving trip meets guidelines under general license for US to travel to Cuba?
Did you read #19 here?
https://www.lonelyplanet.com/thorntree/forums/americas-cuba/cuba/cuba-branch-faq?page=2

Any issues w/proving trip meets guidelines under general license for US to travel to Cuba?
I checked a box on the form, happened to be th same sheet that the agency used to get me the tourist card as well.
The airline did enter my reason for travel into their computer at departure.
I kept no records as such. (Of course, my "reason for travel" is one that does not speak to outsiders about activities.)
When I got back, the US official asked me where I'd been and wished me welcome home.
I do not expect, from a ll reports I have read, that the US government would track me down looking for any "proof" in the coming 5 years.