What is the difference between apartment and holiday home?

Apartment (condominium) is the space in the building, "the box in the air". Holiday home could be the House, guest house, for example.

The difference between the two is not important on Booking as the system unites those two. Most probably you don't like the filter on the left, that combines them into one type. It doesn't make a big impact to guests, as normally they choose in between hotel verses non hotel. Anyway the guest will see your type from title, photos and description.

As per setting your property type, you can do it in extranet.