Wikipedia
De fide (of the faith) is a " theological note" or "theological qualification" that indicates that some religious doctrine is an essential part of Catholic faith and that denial of it is heresy.
The doctrine is de fide divina et ecclesiastica'' (of divine and ecclesiastical faith), if contained in the sources of revelation and therefore believed to have been revealed by God (de fide divina'') and if taught by the Church (de fide ecclesiastica). If a doctrine has been solemnly defined by a pope or an ecumenical council as a dogma, the doctrine is de fide definita.
What is believed to be a truth contained in the sources of revelation thus becomes a " dogma", in the present ecclesiastical sense of this word, only when enunciated by the Church: "According to a long-standing usage a dogma is now understood to be a truth appertaining to faith or morals, revealed by God, transmitted from the Apostles in the Scriptures or by tradition, and proposed by the Church for the acceptance of the faithful."