What is business domain?

So I've read books about "Domain Driven Design" architecture,
most of the thoughts coming to my mind during reading process are where should I put these fraction of code to? And wonder that everyone is also having this problem.

Then, I concluded that you will put everything related to "Business logic" into "Domain layer"

Next question comes to my mind, "Are these fraction of code business logic ?"

FU.. it's a hard question, I even let my friends look at the code and ask them is it the "Business logic" or not, not to be surprised, their answers diverted and with different reasons at that.

Confused, really confused.

Then I found this "Vertical Slice Architecture" (ref. https://jimmybogard.com/vertical-slice-architecture/) invented by Jimmy Bogard, and went through some of his talks.

Finally, I got the idea that every thing is "Business logic", don't spend a lot of time arguing where should we put the code to, put it in plainly first then the important step is later "Refactor" it.

That's it !!