Well "Jaza'ak ALLAH" is used when otherwise people would say 'thank you'.

Well "Jaza'ak ALLAH" is
used when otherwise
people would say
'thank you'.
So it
would mean
something similar to
thank you.
Now 'jaza' is the
opposite of 'saza'.
Saza, as u know, is
punishment, and jaza,
is reward.
So "Jaza'ak
ALLAH" means,
(May
ALLAH Reward You).