"Burn Notes" are sent with an expiration date for their display. The sender can set the viewing time for the recipient to read it. When expired, the note is dynamically erased from the screen and not available more.
Is there a better way to send secret plans or nasty messages that do not leave a paper trail? According to the website, Burn Notes are not just deleted from the screen, but from the server as well in a way that they cannot be recovered. Also, the recipient cannot take a screenshot and cannot copy and paste the notes, if the sender selects the "Spyglass" option. Unread notes are deleted after 72 hours of sending.
Of course, the terms of service state that the messages being sent should not be illegal in any way, which would include, hateful, intimidating or harassing messages.