While high-speed trains (any train with ‘Freccia’ in its name) are usually the best choice for getting around Italy, not every city is served by Trenitalia's AV trains or Italo. cities and towns in Italy are served by regional trains, which are slower and often older trains.
There are a few different names for regional trains in Italy, including (abbreviated with an R on train schedules), Interregionale (IR), Diretto (D), and Espresso (E). Don't be fooled by words that look like “direct” or “express,” these names don't necessarily mean that the train trips are any faster than the trains. Studying the schedule and noting departure and arrival times is still the best way to determine the duration of your train trip.
These trains tend to stop at every single station between two larger cities. Despite the fact that all of these are fairly slow-moving, there is an option known as the Veloce, or “fast regional train,” that makes fewer stops between two destinations.
In certain cases, taking a regional train over the shortest distance by might take you more time than travelling a longer distance on a train with fewer stops, especially if the regional train makes leisurely stops at every little sleepy village on its route.
Regional trains may not be the fastest option, but they're often the least expensive, and for many destinations they're the only choice you will have. It's also important to note that most regional trains only have second-class cars, require no reservations, and may or may not be air-conditioned. It pays to verify these details before booking in order to enjoy the type of travel you prefer.