30 pin 30pin Daughter Board that is under the Extruder Plate.
Acts as a breakout from Larger 30 pin Ribbon cable to the individual Hot end, X axis components
If you have one of the printers that use this, it makes it significantly easier to upgrade your 8 bit board to something better. I wish there was more of a diagram explaining all the connectors on the board and what each pin is. Otherwise great board.
Official Creality CR 10S Pro/ CR 10 Max Daughter Board