Hi there so you were wondering what a double bar line is so i am gonna tell you a double bar line is Answer a double bar line is what music is played on please chose me as best thanks :) always wanting to help you
It is used to denote certain kind of norms in maths. (e.g: ║x║, ║x²║).It's also used to denote parallel lines. And this notation,║A║ is reserved to matrix.Hope it helps.
