Section 230? WTF is that?

Trump is threatening to LITERALLY DEFUND THE MILITARY if he can't get 'Section 230' repealed. What is it?

Ken White says:

Very simply put, Section 230 is the law that says that, if I post something defamatory on Twitter, the victim can sue me, but not Twitter. It also says, again put simply, that Twitter has the right to moderate stuff on its site as it sees fit.

Also, Section 230 Is The Subject of The Most Effective Legal Propaganda He's Ever Seen.