What does this symbol mean?

[Swedemike]

I am trying to apply an effect to a precomp, but it doesn't work the way it works on the other precomp in the project (I am adding things to a template from Motion Array). The thing that the other precomp has is this icon next to it, see enclosed image... What does that icon indicate? There is nothing in the effects control-tab, nothing in the Track Matte and I have un-hidden all hidden features...

[Mylenium]

It is a track matte icon.

Track Mattes and Traveling Mattes

Mylenium