Apart from those good for only a specific journey, at a specific time and date, other tickets
are "open" - and can be used whenever the holder chooses.
To prevent fare evasion by people using the same "open" ticket again and again, passengers are
required to "Validate" these, by stamping them in the machines onboard buses and trams, or at
the train station, etc.... a process that prints on them the travel date and time.
If there's no machine, or it's not working, or you can't get to it, then it's incumbent on you
to validate the ticket manually - by completing the boxes you'll find on the reverse.
See the examples here, from Ischia, Procida, Naples, Pozzuoli and Salerno...
Note also that all-day and multi-day tickets often require you to write in your name, DOB
or the like - to prevent them being used by, or handed over or resold to, other people!
With cashflow problems that have seen more than one of the area's public transport companies
having to postpone payment of their employees' salaries, a very good explanation is needed to
receiving one of the fines that are imposed on those caught travelling without a valid ticket.