What is the yellow circle in fortnite?

The yellow circle in Fortnite is known as the Storm. It is a dangerous and deadly force field that gradually shrinks throughout the match, forcing players to move closer together on the map. Any player caught outside the Storm will take damage over time until they either die or make it back into the safe zone. The Storm is a crucial element of gameplay that adds an element of urgency and strategy to each match, as players must constantly be aware of its movement and plan their movements accordingly.