I often mix up the term "operation" with the term "method".
Because I think that many software engineers have the same problem, I would like to explain the differences today in this post:

Operation
An operation is the abstract definition of a functionality. So to say operations are only the functions head, not the body / implementation.
They describe (by comment and name) WHAT the function does, but not HOW the function achieves this.

Example:

interface Example {
    /**
    * Executes an example function.
    **/
    public function execute();
}

So typically interfaces may only contain operations but not methods, because they do not implement the HOW, just tell WHAT the operation should do.
The concrete implementation is being done by the inheriting classes.

Method
A method is a concrete implementation of an operation and contains a method body though. The method represents the HOW.

Example:

class ExampleClass implements Example {
 
    /**
    * @see Example::execute()
    **/
    public function execute(){
        echo("Execution successful! Have a nice day :)");
    }
}

I hope to help you with my little explanation / definition.