This page explains prefinded variables

"Predefinedd variables are known as superglobals that are special built in arrays created automatically by the PHP engine whenever a script runs." They will be accessible throughout the script.
For example: $serv_name = $_SERVER["Server_Name"]:
The sever's host name is rblee.soisweb.uwm.edu
another example is $GLOBALS. When using variables in other functions, you can still use these in others. Using $user = "Alex" and $score = 100 as variables
The current user is Alex and their score is 100