What Does This Black Square Icon Mean Next to Layer Name?

[AlluringImminence]

Hello, still learning a bit of After Effects, and I am looking at a composition that I downloaded and it has the following icons next to the layer names:

I know the first one is a shape layer mask. But layer 14 is text that is what? Also masked, or what does that black box mean next to the layer name?

Thanks!

[RobShultz]

That icon is an indicator  of the luma track matte of the above layer. Layer 14 would be most opaque on the whitest parts of layer 13 and more transparent the darker layer 13 becomes.

[Warren Heaton · Accepted solution]

The icon to the left of the name identifies the layer's role in a Track Matte.  Layer 13 shows the icon for a Matte Layer while Layer 14 shows the icon for a Fill Layer. 

-Warren