I've been struggling to understand some concepts and examples because they implement a timer ID in them and I don't really get what it is. Is it just a variable you assign a timer to?
Assuming JavaScript because of the "settimeout" tag you added, setTimeout and setInterval return an ID if they succeeded in being setup. This ID can be used to refer to that timeout or interval. Generally, this is used to cancel a timeout before it finishes, or stop an interval from running again. You can do this with the clearTimeout and clearInterval functions.
More information: https://developer.mozilla.org/en-US/docs/Web/API/WindowOrWorkerGlobalScope/setTimeout
In the future, you can find information like this very easily with a search engine.