D5 may represent the square in chess, in Column 4 (D) Row 5. Early game chess often have multiple pieces that can attack that square simultaneously. You want to have more pieces able to attack that than the opponent in order to control that square. I'm not going to pretend like i know chess strategy in depth, but that should give you enough info to be able to research more yourself if you want.

In the video it stands for the first 5 digital countries. Plans for CBDC, total surveillance, digital IDs that kind of thing.

D(E-1)(C-2)(L-3)(A-4)(S-5)

Also Avalanche:

Historic avalanches are D4 and D5 avalanches that can destroy a railway car, large truck, several buildings, a small village, or a forest area up to 40 hectares.

https://www.sierraavalanchecenter.org/how-to-read-avalanche-advisory