So what is the definition that astronomers use to describe it. Well, it is simple. It is the zone where planets orbit and can have liquid water on them, at least part of the time. That weeds out a lot of planets but not as many if the definition was that they had to have liquid water on them. No, they don't need to have water and they don't need to be inhabited. They only need to be orbiting at a distance from their star (sun) that the climate is not too hot nor too cold to have liquid water. Does this make sense to you? I tried to describe it as best as I could.
So, if astronomers were searching for signs of life somewhere where our probes have not reached or may never reach, they could eliminate any of the planets that are not in the "habitable zone". Of course, we must also assume that the life we are looking for is similar to what we are used to here on Earth. Life could take other unusual forms and may not be carbon based as is all life here on Earth. They may be silicon based, or some other chemical base. Or they may be alive in some other way, a way we can not imagine. I don't care what my readers are made of, I like each and every one of you and I want you all to have a great day, you hear?