What does the $\|^2_F$ represent in the notation $\operatorname{argmin}\left\|\text{some expression}\right\|_F^2$?

Question

What does the $\|^2_F$ represent in the notation below $$\operatorname{argmin}\left\|\text{some expression}\right\|_F^2$$

I understand that $\operatorname{argmin}$ is the min of this expression. Generally the Frobenius Norm is notated by underscore F and the L2 norm by a two. But unsure what these expressions mean combined.

Thanks so much