Days in the calendar of the church year for which a liturgical observance is allowed but not required (BCP, pp. 17-18). Sundays, principal feasts, and other holy days always take precedence over any optional days or festivals. Days of optional observance include the various commemorations in the calendar (that is, the "lesser feasts"), other commemorations-not in the calendar-that would use the common of saints, ember days, rogation days, and the "various occasions" for which propers are provided. The days of optional observance, the "lesser feasts," are sometimes called "Black Letter Days," from the English Prayer Book style of listing principal festivals in red and lesser festivals in black.
Days of Optional Observance
Glossary definitions provided courtesy of Church Publishing Incorporated, New York, NY,(All Rights reserved) from "An Episcopal Dictionary of the Church, A User Friendly Reference for Episcopalians," Don S. Armentrout and Robert Boak Slocum, editors.