Tickets that don't include a reservation are also known as open tickets.

These train tickets are valid for a specific route and can be used to board any train that runs on this route that does not require a reservation. It's quite flexible because you can decide which train to take after you've bought the train tickets. With open tickets, you do not have a pre-assigned seat. You can sit in any available seat in the class of service your train ticket was issued for.

Open tickets are valid for one month from the date of issue. The validity dates will be printed on the tickets. You can travel with an open ticket on any date within the validity period (however, remember: separate reservations may be necessary, depending on the route).