black dot on reservation calendar?

[Michael389]

Anybody know what a big black dot indicates when it appears on the arrival date of a guest on my calendar? 

[Lawrene0]

Without a screenshot, I'm just guessing, @Michael389, but maybe it is the guest's profile picture? Did they use just a black circle maybe? What happens when you click on it?

[Antra12]

This means popular dates https://airbnbase.com/black-dots/