What is the difference between === and == ?

output of "==" can be 1, 0 or X.
output of "===" can only be 0 or 1.
When you are comparing 2 nos using "==" and if one/both the numbers have one or more bits as "x" then the output would be "X" . But if use "===" outpout would be 0 or 1.
e.g A = 3'b1x0
B = 3'b10x
A == B will give X as output.
A === B will give 0 as output.
"==" is used for comparison of only 1's and 0's .It can't compare Xs. If any bit of the input is X output will be X
"===" is used for comparison of X also.