What Do the Ellipses in the Tight Binding Model Equation Represent?

[disclaimer]

I'm reading my lectures on TBM and I don't understand the following thing:

$$\omega(\overrightarrow k)=\omega_0-4t\cdot[\cos(k_xa/2)\cos(k_ya/2)+...]$$

It's related to FCC structures, in which the number of Nearest Neighbors $$(Z)$$ of an atom is equal to 12. Basically the three dots at the end leave me puzzled. What are they supposed to mean? Any help appreciated.

 

[weejee]

I guess just the cyclic permutation of (k_x, k_y, k_z)