What does “initial form” mean in “Received:” header definition of RFC822?

Question

As follows, RFC822 refers "Received:" header's "for" parameter as "initial form".
What does "initial form" mean? The word "initial form" is too generic.

received    =  "Received"    ":"            ; one per relay
                       ["from" domain]           ; sending host
                       ["by"   domain]           ; receiving host
                       ["via"  atom]             ; physical path
                      *("with" atom)             ; link/mail protocol
                       ["id"   msg-id]           ; receiver msg id
                       ["for"  addr-spec]        ; initial form
                        ";"    date-time         ; time received

Answer 1

AFAIK "for" part of Received: header (optionally) provides track of recipient address (at SMTP session level).