There are some few silent prayers in the Novus Ordo, but very few and i even think they are optional.
Anyway…
The Secret (
Latin Secreta, sc. oratio secreta) is the
prayer said in a low voice by the celebrant at the end of the
Offertory in the Roman
Liturgy. It is the original and for a long
time was the only
offertory prayer. It is said in a low voice merely because at the same
time the choir sings the
Offertory, and it has inherited the special name of Secret as being the only
prayer said in that way at the beginning. The
silent recital of the Canon (which is sometimes called “Secreta”, as by Durandus, “Rat. div. off.”, IV, xxxv), did not begin earlier than the sixth or seventh century,
Cardinal Bona thinks not till the tenth (Rer. liturg., II, 13, §1). Moreover all our present
offertory prayers are late additions, not made in
Rome till the fourteenth century (see OFFERTORY). Till then the
offertory act was made in
silence, the corresponding
prayer that followed it was our Secret. Already in “Apostolic Const.”, VIII, XII, 4, the celebrant receiving the
bread and
wine,
prays “silently” (Brightman “Eastern
Liturgies”, p. 14), doubtless for the same reason, because a
psalm was being sung. Since it is said silently the Secret is not introduced by the invitation to the people: “Oremus”. It is part of the Proper of the Mass, changing for each
feast or occasion, and is built up in the same way as the Collect (q.v.). The Secret too alludes to the
saint or occasion of the day. But it keeps its special
character inasmuch as it nearly always (always in the case of the old ones) asks
God to receive these present gifts, to sanctify them, etc. All this is found exactly as now in the earliest Secrets we
know, those of the Leonine Sacramentary. Already there the Collect, Secret,
Postcommunion, and “Oratio ad populum” form a connected and homogeneous group of
prayers. So the multiplication of Collects in one Mass (see COLLECT) entailed a corresponding multiplication of Secrets. For every Collect the corresponding Secret is said.
newadvent.org/cathen/13673b.htm