I agree with "Board" because of terrain. Maybe something even more generic like "Playing Field", except that I prefer the brevity of "Board".
I also prefer the brevity of Board. While the word might most literally refer to a contained 2D playing area, Chess variants are classed as board games, and the word is normally used for the playing area in any Chess variant, even if it doesn't follow the planar geometry of a literal board.
I also prefer the brevity of Board. While the word might most literally refer to a contained 2D playing area, Chess variants are classed as board games, and the word is normally used for the playing area in any Chess variant, even if it doesn't follow the planar geometry of a literal board.