The difference between censorship and moderation is the ability to realistically opt-out. Your friends might get mad at your for saying something, but you can choose your friends. Your community might not allow certain speech, but you generally get to choose the communities you are a part of. When the avenues where 99% of all communication go through "moderate" speech a certain way, that starts being censorship.

The difference is somewhat part who is doing the moderating, but it is far more important the ability to opt-out without significant negative impact.

That isn't the reality of moderation. Often moderation effectively acts as a form of censorship, and the two work together. Often moderators either power trip or misunderstand the situation and allow bad actors to abuse the rules to their advantage to have people shut out of the group.

This happens, btw, when there are the most rules and heavy-handed moderation. Places that are less moderated, this rarely happens because people will directly call this behaviour out and the moderators are only intervening on important stuff, e.g., threats of violence, illegal material, etc.

Those sounds like largely unrelated concepts that just happen to overlap somewhat in practice, and are also very individual. As a private person I don't lose anything at all by not using social media, but if I owned a local pizza shop I'd be losing a ton of business by shunning hat avenue of advertisement.

Personally I think the most useful definition for censorship in the context discussed here is *government* censorship. A company offering a product isn't forcing you to engage with it, even if it is a benefit to do so. You cannot in any way evade the oversight of your government without risking criminal penalties. Amazon can deny you their services. The government can deny you your life and freedom.

It's why the 1st Amendment protects us again government control of speech and assembly, but not the censure and pressure of our peers.