d5?

The founding members of the Digital 5 group are:[4]

Estonia

Israel

New Zealand

South Korea

United Kingdom

what else could d5 relate to? https://en.wikipedia.org/wiki/Digital_5

d5? A Closed Game (or Double Queen's Pawn Opening) is a chess opening that begins with the moves:

1. d4 d5

The move 1.d4 offers the same benefits to development and center control as does 1.e4, but unlike with the King Pawn openings where the e4 pawn is undefended after the first move, the d4 pawn is protected by White's queen. This slight difference has a tremendous effect on the opening. For instance, whereas the King's Gambit is rarely played today at the highest levels of chess, the Queen's Gambit remains popular at all levels of play. Also, compared with the King Pawn openings, transpositions between variations are more common and important in the closed games.