When an object is passed as an argument to a method what is passed into the method?

I will call what you are passing in a to a function the actual parameters, and where you receive them, the parameters in the function, the formal parameters. They are also called actual and formal arguments.

When passing parameters, what it is called and what happens can be confusing. It is less essential that you call it the "correct" thing than you know exactly what is happening. It is critical to have a good mental model, a valid memory picture of the process.

Recall that when you call a function, a chunk of memory called an activation record is allocated. Critical to the discussion here is that this memory holds the formal parameter values and function local variables.

By definition, pass by value means you are making a copy in memory of the actual parameter's value that is passed in, a copy of the contents of the actual parameter. Use pass by value when when you are only "using" the parameter for some computation, not changing it for the client program.

In pass by reference [also called pass by address], a copy of the address of the actual parameter is stored. Use pass by reference when you are changing the parameter passed in by the client program.

Consider a swapping function to demonstrate pass by value vs. pass by reference. This function, which swaps ints, cannot be done in Java.

   main[] {
      int i = 10, j = 20;
      swapThemByVal[i, j];
      cout