Title 26 is the law. I just gave it to you. You can't cite a website in a tax matter, even if the website is that of the IRS.

It also depends on the section of the law you're looking at. For example, the website you're referencing has to do with non-profits.

Right.  But, whatever you cited, seems incomplete.  Thats all.

For instance, is the definition at the link below, created in a law somewhere?

https://www.irs.gov/charities-non-profits/trade-or-business-defined:

jeff

In statutory law, legal definitions prevail in the section in which they are defined. 

kytt

bitcoin

New Bitcoin tax reporting obligations took effect on new year’s day

Rsync25

I don't think you cited a glossary definition of "trade or business".