Is there a name for X Day of the month?

Im working on a form for a feature for a report that can have its frequency scheduled set by the user. One of the requests from our product owner is that the user is able to set frequency by a monthly option that is "on the third wednesday" of the month. How would this be described in the options?

a On the X day of the month

b "Week of the Month", "Day of the Week" ie. "1st Monday"