How does the Optimistic Habitable Zone differ from the Conservative Habitable Zone definition?

It accounts for planets possessing thick, highly efficient greenhouse atmospheres

Astronomers employ multiple definitions to assess potential habitability, leading to the distinction between the Conservative and Optimistic Habitable Zones. The Conservative HZ represents the most strictly defined region where liquid water is highly probable based on minimal atmospheric assumptions. In contrast, the Optimistic Habitable Zone extends these boundaries further inward and outward. This extension explicitly considers theoretical scenarios where a planet possesses a significantly thicker atmosphere, perhaps rich in greenhouse gases, allowing it to retain liquid water even when it is receiving less stellar energy (at the outer limit) or more energy than a planet with Earth's current atmosphere (at the inner limit).