note - the original post

reply - A note reply to the original note, with content after the note id referenced. Can be threaded as it references all prior notes

quote-note - A note you create that reference's another note, and adds personal context before the note id. Starts a new note thread

boost - When you see someone else's note, and you create a new note that includes the note id, and no new content

renote - A self boost of your own note, without new content

broadcast - When you see someone else's note, and you send it to the relays you can write to, without creating a new note