Is there a name for the X day of the month?

I am working on a form for a function for a report that may have its frequency programmed by the user. One of the requests of the owner of our product is that the user can establish the frequency by means of a monthly option that is performed "on the third Wednesday" of the month. How would this be described in the options?

a The X day of the month

b "Week of the month", "Day of the week", that is. "1st Monday"