On the Eurail timetable InterCity trains are listed as "IC", and Trenitalia regional trains as "R". Trenord regional trains are only shown on the Trenitalia timetable and not on the Eurail timetable. They are named "Regionale". Regional trains do not require seat reservations. Reservations are however mandatory for InterCity trains during high season (May - September) and public holidays.
On the Eurail timetable shows Frecciarossa trains as "FR", Frecciargento as "FA" and Frecciabianca as "FB". The Trenitalia timetable lists the specific Italian name, e.g. "Frecciarossa". These trains always require a seat reservation.
ÖBB Nightjet appears as "EN" in the timetable. InterCity Notte appears on the Eurail timetable as "ICN". On the Trenitalia timetable it is simply listed as "InterCityNotte". You are required to book sleeping accommodation in advance.