Today is not a universal holy day of obligation in the Catholic Church; in most places, it is just a regular weekday of Advent with the usual Sunday obligation applying only to Sundays themselves. In 2025, the remaining holy days of obligation in December are December 8 (Immaculate Conception, which is a day of obligation in many countries) and December 25 (Christmas), not December 9 or 10.
If a priest, parish bulletin, or local calendar is saying today is a holy day of obligation, it is likely for a local reason (for example, a diocesan patronal feast, a parish’s titular feast, or a special celebration) rather than a worldwide rule. The best way to know for sure is to check your own diocesan website or parish bulletin, because bishops’ conferences can add or transfer days of obligation in specific regions.
