What actually is non-penetrative sex?

This might be a dumb question, but I read a lot in this sub about how sex doesn't have to include penetration. I agree but as someone with very little experience I'd like some clarification on what are my other options.

I feel more confident and less anxious when I have all the information. If you don't mind, please could you share what you actual mean by non-penetrative sex or sex without PIV?