Name day is a tradition in some countries, that people celebrates particular given name on a selected day of the year. The celebration is similar to a birthday. You can find out more about this tradition on https://en.wikipedia.org/wiki/Name_day or https://www.behindthename.com/namedays/.
By creating an item with Type “Today’s name day”, Slideshow can display on the screen which name celebrates name day on the current day. Slideshow has an offline copy of the list of names, there is no need to be connected to the internet to display the name.
Source of the names for particular days is this open-source repository: https://github.com/milan-fabian/name-day-list.