Under United States 121 Flag (international) rules the fuel reserve includes, among other things, 10% of the flight time from departure to destination. This can get to be a very large fuel load on long flights. The work around is the “Planned Redispatch”, where the flight is in effect broken into two sections. The first part is from the departure airport to an initial destination, then approaching that point if all is going well the flight is redispatched to the final destination--which starts the fuel reserve calculation over.
An example might be a JFK-FRA flight with AMS as the initial destination. There is no intent to land at AMS, which exists in the planning as only a paperwork exercise. Of course sometimes it does not work out as planned
Much longer explanations are possible, but this is the basics of it.