!=

Not Equals takes the top two values on the regular stack, and places true on the conditions stack if the two values were not equal, false otherwise.

For instance:

50 50 !=

Will place false on the conditions stack. The two 50s are removed from the regular stack.

50 60 !=

Will place true on the conditions stack. The 50 and 60 are still removed from the regular stack.

Logical Comparison Operators: > < >= <= = != %= !%= ~= !~=