An MoC is a Map of Content. Essentially, it’s an index page or table of contents of the entire vault, or a portion of the vault.
I actually refer to mine as index pages, but I thought saying “MoC” would be more clearly understood on this forum. Guess I was wrong about that!
I do an index page per project, which also contain brief status updates on project progress. I also do higher-level index pages grouping related projects together. These higher-level pages are indexes of indexes.