This is a term that astronomers use to describe a region around a star where conditions are right for water to be liquid — and possibly support life. If a planet is too far away from its star, any water would be permanently frozen. If a planet is too close, water would boil away immediately. But is the planet is in just the right place, water could be a liquid.
That doesn’t mean a planet in the zone would be a nice place to live, though. There may not be any water there to begin with. And even if there is, there may not be any oxygen to breathe. Still, a planet in the Goldilocks zone is our best bet in the search for life outside our solar system.
In a sentence
The star Trappist-1 has seven Earth-sized planets, and three of them are in the Goldilocks zone.