Predefined variables are variables that have their own value before the execution of the PHP code. This means that I do not need to set a value to the variable because predefined variables inherently have values, most of which reflect the properties of the server as seen above.
Predefined variables are a bit long and tedious to type out repeatedly though. So that is why I also included examples of storing the predefined variables within standard variables so that it is easier to access their values, which are displayed identically as seen above.