In some table 1 of the crystallography paper, there is an item called "FOM". Will you please explain the meaning of it? Do we have a server to get it or some other route to get this value?

This is the letter "m" in Randy's 2mFo-DFc map -;)

phenix.refine, phenix.maps and other relevant tools estimate it in resolution shells using test reflections as described here:

J. Appl. Cryst. (1996). 29, 741-744

and here

Acta Cryst. (1995). A51, 880-887

Of course there are plenty of other literature on this subject!

Pavel