This reads like an ad. Why would you capitalize it like a product name and then even link to the website?
I still have no idea what it really is. From the name I'd think you're going for a run at a local park. The website calls it a "5k and 2k community event", what that's supposed to mean I have no clue. It insists you either "join" or "volunteer", all while being as non-specific as possible why I should even care
2/5k what? people? distance? currency? number of events? It almost reads like in-group speak of a cult I don't partake in.
-- Rant over --
5k is a common distance for runs. 2k would be a shorter run/walk event, it's more common when you have kids participating. It's not confusing, just normal language. No cults involved unless you think running is a cult. The "k" is for "kilometer" in case you're still confused.
I’m advocating not advertising.
I capitalise it out of muscle memory. That’s all. FWIW Wikipedia capitalises it as well.
I called it out with a link because I expect many folk to be unfamiliar with it, but the nature of parkrun itself — rather than simply going for a 5k[m] run — is intrinsic to the point I was trying to make.
5k is perfectly well understood to be a distance, especially in context, in British English and I’m a Brit. My bad I guess for not adding “m” for (some of) the HN readership. [EDIT: actually, I said 5km! Not my fault if parkrun says 5k, but they are a British organisation)
Regardless of that, you were correct that parkrun is indeed a run around a park. I won’t explain any further nor link anywhere lest it be misconstrued as advertising (something that’s proudly free, mind you). Besides which I need to get to and get my running kit on.