What does such an arrow mean in the window with Photoshop layers?

Question

Adobe Photoshop

Here, in the image noted:
Please tell me

Answer 1

This is a mask.
Those. the top layer has the shape of the bottom.
Here's an example:
I put mine above with a circle and gave it a mask in the form of a bottom layer with a square. This is done by pressing alt between these layers -)