p. 491) In other words, the D in D-Day merely stands for Day. This coded designation was used for the day of any important invasion or military operation.
Many experts have varying opinions, including that the D simply stood for "day," a code used for any important military operation. Others have said it's just alliteration, like "H-Hour," when a military assault begins.
"Generation Break" or "GB" for short (000000000000 Jenershon Bureiku) is a keyword introduced in G Trial Deck 1: Awakening of the Interdimensional Dragon and G Trial Deck 2: Divine Swordsman of the Shiny Star.