BuiltIn.ParamStr Method

not certain but ill give this a shot,

since builtin.paramstr is typically used as a helper method to return the values supplied to run TC via cmd line,

these index numbers (i.e 12, 13, 14) that you've highlighted in the screenshot, are referring to the cmd line arguments that you (or someone in your org) plans on providing to TC. 

Since the function nature of the screenshot you've provided looks to be a helper function designed to log the arguments provided (in specific, it looks to be logging the label of the execution node "slave"), and since the index is hardcoded, i'm willing to bet that there is a stable pipeline (from a CI system) that your org is using to run your TC projects/tests.

So, fastest way to figure out what those numbers mean, i think i'd go into your CI system and read the yaml file or look at the testcomplete test step (which is where you would find the sequence of cmd line arguments supplied), or just trigger a run and see what the log outputs are.