# What does “static” in the context of a SEM mean?

I just stumbled upon a wiki article:

http://en.wikipedia.org/wiki/Endogeneity_(economics)#Omitted_Variable

In the section "simultaneity" theres a description of a model which says that both variables are codetermined ,i.e. each affecting the other, and it's a static SEM

The model is

$y_i = \beta_1 x_i + \gamma_1 z_i + u_i$

$z_i = \beta_2 x_i + \gamma_2 y_i + v_i$

My question is: What does static in this context mean? My guess is that though it's a dynamic model we actually can't observe the dependency between $y_i$ and $z_i$. One would need at least one additional "shifter" in order to observe these dependencies.