The answer to your question might be more complicated than you expected. I'll cover it in two parts, first explaining what a "feast day" is and then talking about the saints and their special days on our liturgical calendar.
A saint's feast day is the special day (or days... some saints get more than one!) that we particularly honor that saint's life on earth and look to him or her as a special example and intercessor. Feast days come in a few different types, some of which are more significant than others. At the bottom of the list are "optional memorials", which individual priests have the option to celebrate or ignore when saying Mass. If a priest wants to honor a saint who is not "officially" on the local calendar on the proper feast day, he will celebrate that saint's day as an optional memorial, but there are also saints whose days are officially listed as "optional". Next are memorials, which work the same way except that they can't be skipped. (They can and sometimes must be replaced with a different feast that falls on the same day.) Next up are feasts, which are actually celebrated a little differently than regular Masses. They sometimes get an extra reading and usually include the
Gloria (which gets skipped on a normal weekday Mass). At the very top are solemnities, which are celebrated just like Sunday Mass even when they fall on a weekday. All of our Holy Days of Obligation are solemnities. And if a solemnity happens to fall on a Sunday, it can even replace the regular Sunday Mass!
Watch this space next week for more about all of the saints and their special days on the liturgical calendar.
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