> 5k is not a distance. 5km, 5 thousand feet or yards are.

I answered that question already, try reading my earlier comment. And if you think it's weird, take it up with people from last century when they started using that abbreviation.

It's extremely common, even in the USA, although in the USA it's more limited to running communities. In the UK, NZ, Australia, road running is common enough that anyone would know what you mean, but it's a bit less of a thing in the USA.

https://en.wiktionary.org/wiki/5K

https://en.wikipedia.org/wiki/5K_run