What makes a project genuinely part of the IndieWeb ?

I've been working on a web project and one thing I've been thinking about is how much of the experience can stay away from the big social platforms.

where the main idea's to see if one million people can take part in the same internet experiment through a very simple individual action.

What I'm more interested in talking about here is the web setup and the way of thinking behind creating something like this on your own.

For people who create their own websites:

What makes you think a project is truly part of the IndieWeb?

Is it being technically independent having your own domain and your own content staying away, from big platforms using open systems or something else?

I'm really curious how others decide where to draw the line because "independent website" and "IndieWeb project" don't always mean the thing.