I won't repeat the excellent definitions already provided, but can share some examples of class parameters where we use them:

Parameter FILES = "/files";
Parameter INSTANCE As COSEXPRESSION = "$p($SYSTEM, "":"", 2)";
Parameter RUNLEVEL As COSEXPRESSION = "$li($lb(""dev"",""Test"",""LIVE""), $lf($lb(""HCDEV"",""HCTEST"",""HCLIVE""), ..#INSTANCE))";

We use ..#FILES to prefix or normalize a directory off the top-level filesystem on the server.

We use ..#INSTANCE if we need to identify which IRIS instance, like in an email message, it came from.

We use ..#RUNLEVEL in conditionals or pass as a parameter, where we might want code only to run on "Test" or "LIVE".

lol, reading is fundamental.  Thank you for pointing out what should have been obvious.

I missed the "User" in your example as a custom implementation.  I just reviewed these provided adapters, very nice!  What continues to puzzle me is why the product does not provide a Business Operation off them (and others).  I know, support issues, right?

I just completed a custom "adaptation" using their provided Util.Pipe adapter, because the code was a bit crusty.  It did serve as nice reference source, just not as nice as these SQL adapters.

There's a plethora of ways to get license information, as Marcel pointed out, through $SYSTEM.License.  The online class reference show the methods and queries, with sample code, available to invoke: https://docs.intersystems.com/latest/csp/documatic/%25CSP.Documatic.cls?...

From a command-line (list instance name(s) running, i.e., CACHE) that can be setup to run as a secure remote procedure call; or what we do is have scripts that feed back this data to our Nagios monitor for hosts/instances:

$ ccontrol all
$ ccontrol stat CACHE -a0 -L1

Hope this helps.