LARTC - Jan 2002 - what does this stand for ?

hi

tc filter add dev eth0 protocol ip parent 1:0 prio 1 u32 \
   match ip src 1.2.3.4 match tcp dst 80 0xffff flowid 1:10

in the above command i would like to know what does the string
"0xffff"
stand for, i know it is explained in adv. routing howto''s u32 section; 
but i could not make any heads or tails of it. can some explain in 
detail any links would also do.

thanks
shekhar