Hi, 

local trains like regional trains are in most cases included. Some times also Suburban trains when they are run by an train company, like suburban trains in Berlin, Munich or Vienna.

Underground/Metro, Tram, Bus are NOT included.

To use trains you need a valid pass and they count as travel day. Only trains where you get only a discount you have not to use a travel day (keep in mind that reservation cost are not a discount, and so it counts as travel day).

In your case, you can use all local trains and IC trains in Belgium (without reservation but with using a travel day and adding the trip to your pass). 

In Italy all local trains (regionale and regionale veloce/regio express) are included with this exceptions: Malpensa Express to Milan Malpensa Airport is not included, Leonardo Express to Rome Fiumicino Airport is included only with 1st class Pass.

Regional/local trains of Circumvesuviana and EAV in Neaples are not included, but they are cheap like most regional trains in Italy. 

Metro line 2 in Neaples is included, because it is a train service run by Trenitalia, and included in the pass.

You need a valid travel day to use any train.

Apart from trains, only rail replacement buses and maybe 1 or 2 other bus lines. In Switzerland also a few ferries. Check the country pages for details.

Many countries also offer their on passes-at lower prices or for certain trains/areas only, or may give generous age-discounts. These may lower your total outlay, but this is such a complicated mess that untill now I have never seen even a global overview on them.

On a global continuous longer time pass the cost per day (like for me currently just 5€, 3 month bought with the jubilee 50% discount) can be so low that this would also make no sense.