What is the difference between doctrine and dogma?

In general, doctrine is all Church teaching on faith and morals. Dogma is narrower: the part of doctrine that is divinely revealed and that the Church has formally defined and declared must be believed as revealed.

The Catechism says the Magisterium exercises Christ's authority most fully when it defines dogmas: when it proposes, in a form obliging Christians to an irrevocable adherence of faith, truths contained in divine revelation, or truths necessarily connected with them, in a definitive way (CCC 88).

For example, the teaching that Mary is Mediatrix of All Graces is divinely revealed but has not been raised to a dogma, though it could be. Ludwig Ott writes in Fundamentals of Catholic Dogma that her universal mediation of grace, based on her cooperation in the Incarnation, is so clearly manifest in the sources of faith that nothing stands in the way of a dogmatic definition.