What does this mean in the offer letter In my offer letter:


  $XX,XXX is being offered as "for Spring and Fall semester for the year 20XX"


Here what do they mean? Is $XX,XXX being offered on a per month basis or for the whole year?
From your comment, $MMM is on the order of US$20,000.  This is almost certainly the stipend for one academic year.

It will probably be paid in monthly or semimonthly installments, over 9 or 12 months.