Often you will see the word “Memorial” in the title of one of the Daily Readings’ posts.
For example, today is the commemoration/Memorial of St. Teresa of Jesus, formerly, St. Teresa of Avila, Virgin and Doctor of the Church.
On a Memorial, the priest uses the Sacramentary for that day, invoking special prayers during the Mass that commenorate the Saint.
On an Optional Memorial, the priest may choose to follow those specific prayers for that saint or may do a regular Mass of the season. Yesterday was the Optional Memorial of St. Callistus I, Pope and Martyr.
I always mention the “memorial” if there’s one listed when we read the daily lectionary, and sometimes we look up the saint.
When did they change St. Theresa’s name?
In my experience there is usually very little mention of that day’s saint(s) at daily mass, slightly more of there is “major” saint on that day. I often wish the priest would spend some time talking about what we can learn from the saints. Sort of a “practical guide to a Christian life”.