SIMPLE
It's a prefix to indicate the number is in hexadecimal rather than in some other base. The C programming language uses it to tell compiler.
Example :
0x6400
translates to 6*16^3 + 4*16^2 + 0*16^1 +0*16^0 = 25600.
When compiler reads 0x6400
, It understands the number is hexadecimal with the help of 0x term. Usually we can understand by (6400)16 or (6400)8
or any base ..
Hope Helped in some way.
Good day,