If you want to know what cyber security is, you can ask me, and I’ll tell you: it’s the thing I do (among other things) for a living. But if you want to know what cyber security is, it’s not enough to ask me; you also have to think about the answer.
What is cyber security? It’s a question like „what is cyber security explain is pornography?” or „What is art?” I could tell you what (some of) my friends think it is, but that wouldn’t be enough; we’d need to stop there and think, then come back together and talk some more about whether our ideas match.
If we did that, we’d probably figure out something like this:
Cyber security is protecting computers so that they continue doing useful things for us.