System aka Environment Variables
System, also known as environment, variables are values that the operating system uses to run processes. Important facts to be aware of:
-The primary use case for environment variables is to limit the need to modify and re-release an application due to changes in configuration data.
-At runtime, the reference to the environment variable name is replaced with its current value.
-An environment variable is a variable whose value is set outside the program, typically through functionality built into the operating system
An environment variable is made up of a name/value pair, and any number may be created and available for reference at a point in time. (so does this mean we can make up our own?)