In mathematics can be used for a unknown value like in algebra.
It can signify multiplication such as 4 x 5 = 20
Those of you born after 1981 (the baby boom) are know as Generation X
and this signifies to sign here.
X.......... the Roman numeral for 10
If you are a bowler you want to see lots of x's on your score sheet signifying strikes!
In sign language this is the sign for debt...