What is heavily obscured 5e?

In heavily obscured conditions in 5e, a creature's vision is completely blocked or severely impaired. This can be caused by darkness, fog, smoke, or similar environmental factors.

Under heavily obscured conditions, creatures are considered effectively blind, meaning they cannot accurately perceive their surroundings. They have disadvantage on attack rolls, and attack rolls against them have advantage. Additionally, creatures have disadvantage on Wisdom (Perception) checks that rely on sight and automatically fail Wisdom (Perception) checks that rely on smell.

Some spells and abilities can create heavily obscured conditions, such as the fog cloud spell. Certain creatures, such as those with blindsight or tremorsense, may not be affected by heavily obscured conditions.