Free Running is a movement mechanic in Kingdom Hearts III. Based on Flowmotion from Kingdom Hearts 3D: Dream Drop Distance and utilizing mechanics from Kingdom Hearts 0.2 Birth by Sleep -A fragmentary passage-, it allows Sora to seamlessly navigate the environment such as short gaps and ledges without extra input from the player, as well as allowing him to run up walls which are faintly glowing by running against them.
The return of a Flowmotion-like ability was first shown briefly during the Jump Festa 2016 trailer, and was expanded on in later trailers. The Orchestra -World Tour- trailer in June 2017 showed Sora running on walls during the Rock Titan fight for the first time. Tetsuya Nomura revealed the new mechanic's name as Athletic Flow in an interview with Gameinformer a month later.
In a gameplay demo presented to the press in May 2018, a tutorial screen revealed the name Autorunning for the English version of the title, and described it as allowing Sora to "climb up small ledges and hop across narrow footholds." However, in the final game, the name was changed to Free Running.
↑ 1.0 1.1 GameInformer: "Nomura Reveals More On Kingdom Hearts III's Keyblade Transformations And Summons", Nomura: "It's a new mechanic that we're implementing in Kingdom Hearts III. The Japanese name is Athletic Flow. I don't know what the English final name is just yet. It's based on the Flow Motion mechanic, and it's basically revamped and introduced as a new mechanic in Kingdom Hearts III. You'll be utilizing the environment to propel yourself to an area that you're not normally able to go to, or again, running up the cliff during battle. Those can be expected in each of the different worlds you'll be traversing through."