A ghost ping is a message that pings someone and is deleted by its author within a minute. Defendr logs it as a card in the Messages log category with the author, the channel and who was pinged; the text itself is never stored. Deletions by moderators are not ghost pings: Defendr checks the audit log for a moderator deletion first. Without the View Audit Log permission, or when the check could not run, the card says "possibly a moderator deletion". Replies that only ping the person replied to are ignored, and so are Defendr's own deletions.
Example
/setup › Find a setting › Ghost pings