OP_0NOTEQUAL checks whether the top item on the stack is not zero. If the top item is any nonzero value, OP_0NOTEQUAL pushes 1 (true) onto the stack; if the top item is 0, it pushes 0 (false). This opcode is useful in conditions where the presence or absence of a value is to be checked, essentially serving as a nonzero check.
OP_Code Walkthrough
Checks if the top item of the stack is not 0
Pop Top Item
Check if item is not 0
Push Result