что означает 2.5 bathrooms в объявлении ?

Могу ошибаться, но, по-моему, это значит, что есть две полноценных ванных комнаты (с ванной, умывальником и туалетом) , и одна, где есть лишь унитаз и рукомойник (то есть без душа и ванны) .

Да, так и есть, вот цитаты, подтверждающие это:

One method is to count a half bathroom as ".5" and then add this to the number of full bathrooms (e.g., "2.5" baths would mean 2 full baths and 1 half bath).

No need to wrack your brains and tax your design skills when dealing with the half bath. In most cases, you only have a small area to work with, which means that there isn't a whole lot of stuff you can put into a half bath. No shower, no bathtub, no extensive counters.

A half bathroom is a bathroom which has a sink and a toilet, but no shower or tub. Such rooms are sometimes known colloquially as “half baths” or “powder rooms.” Many larger homes include a built in half bath, typically in a public area of the home so that it is readily accessible to guests. Especially in a house with multiple residents, a half bathroom can be an extremely useful thing, as it reduces pileups at the main bathroom in the morning, allowing people to use the toilet while leaving the shower free.

В объявлении чего?

ванная комната 2.5 наверное площадь