What is the difference between a reply and a private note on a ticket?

A reply is sent by email to the ticket's recipients (To, CC, BCC) and becomes part of the customer-facing conversation. A private note is internal only: it is never emailed, the recipient fields are hidden while you write it, and it is shown in the thread with a dashed border and an eye icon so users can tell it apart. You switch between the two with the "Reply" and "Private note" tabs above the editor.