A long time ago, this site was called "Startup News" and it focused on topics related to tech startups... so, basically, computers, programming languages, the Internet, etc., + business topics: sales, marketing, fundraising, etc., but with a heavy focus on stuff like "how to raise a round" and how to negotiate VC terms" and things of that nature. There was also plenty of general business news, focused mainly on SV companies and famous/big tech companies.
Later it became "Hacker News" and the focus seemed to largely stay mostly the same for a long time, with a slight widening of focus to include maybe more general science / tech stuff, not just stuff related to startups.
Over time, the focus has broadened even more to where some of the early stuff is pretty de-emphasized (you don't see as much fundraising advice now, for example) and you get a lot more general news, politics, world events, etc.
What's "on topic" is described pretty broadly in the guidelines[1] as "anything that gratifies one's intellectual curiosity."
OTOH, the guidelines also say "Off-Topic: Most stories about politics, or crime, or sports, unless they're evidence of some interesting new phenomenon. Videos of pratfalls or disasters, or cute animal pictures. If they'd cover it on TV news, it's probably off-topic."
But yet we still get a fair amount of political content here, and more than a little bit of stuff that probably is covered on TV news. But we still manage to avoid "cute animal picture" and generic reddit/4chan style memes and shit at least.
[1]: https://news.ycombinator.com/newsguidelines.html