Each region is divided into a number of "rungs", essentially just groups / leagues / divisions of the regional ladder. Rungs do not affect movement on the ladder, so if you can happily ignore them if you want and Ladder will function the same for you as it always did.
Rungs were needed was as a way to reintroduce (May 2025) Belts to the Ladder. Belts are a challenge system much like in Boxing or similar sports, where a challenger can win the belt by defeating the current holder. Each Rung of the ladder now has a Belt associated with it. Anyone in the same Rung is entitled to challenge the belt holder for that rung. Potentially allowing you to win and move up the ladder by quite a large number of teams.
The actual rules on this become complicated pretty quickly, as normal ladder movement happens, some belts will be in the "wrong" rung. If this happens, anyone from the rung the belt is from can still challenge the team. However, the next time a belt holder races - if they are not in the correct rung -- they will lose the belt. (If the challenger to them is in the correct rung, they will receive the belt even if they are the losers. If both teams are out of the correct rung, the belt will be handed to someone within the correct rung instead) Belts also will be "dropped" by a holding team after 14 days if they don't complete another race. (Note currently, you must race in that 14 days, if you have a match-up on the 15th or 16th day, you will already have lost the Belt by then)
There are two new pages "Rungs" and "Belts" under the "More" option in the navigation bar, or just visit "/rungs" and "/belts" on the site.