Field status determines how a field is displayed or 
maintained. 
Field status variant is a collection of field status group.
Field status group means -
a) Combinition of field statuses for a group of fields.
b) Defines the screen layout at the time of document entry 
at line item level.
c) Assigned to each G/L A/C.

Conclusion:- Combination of field status groups maintained 
in field status variant.

Plz, let me know anything more if i am wrong? to all sap 
gurus.

above answer is c orrect

Field status group is controls the apperance of your screen 
when you are posting a document. Collection of field status 
groups is field status variant.

field status group differenciate a set of field status in 
every g/l account it contain in posting in  gl account and 
account type.
and field status varrient is a set of field status group 
with control on fields as required, optional or suppress
i am wrong pls correct me