noun
h1-a8 diagonal (in Othello)
A term used in the board game Othello (Reversi) to refer to the diagonal line from square h1 to a8. This is a domain-specific term familiar to Othello players.
from English black line
オセロでは、ブラックラインを制することが重要だ。
In Othello, controlling the black line is important.
彼はブラックラインに石を置いて、形勢を逆転させた。
He placed a piece on the black line and turned the game around.