Composite Functions Symbol?

Composite Functions Symbol?
I need to know what those 3 dots are

http://i50.tinypic.com/2q3uof8.jpg

I dont understand the term

The composite function symbol is the o in between dg and f. It's actually in the incorrect spot there, but I guess that's an alternative writing.
It's usually seen like this:
(f o g)(x)
The o stands for "of."
(f o g)(x) = f of g of x = f of g(x) = f(g(x))

Although I can't tell if that image is saying that d is a function or a symbol denoting something else.
I assumed it meant: d of g of f = d(g(f)).
But maybe it stands for derivative?
d modifying g(f(x)) where x is implied in that writing.

The image is pretty vague.

And yes, the three dots means therefore.