Demarcation line

Okay, so when you have two friends who are playing with blocks and they start arguing over who gets to play with which blocks, sometimes they need a grown-up to come in and help. The grown-up might put a line down the middle of the playing area with a piece of tape or a marker. This line is called a demarcation line. It shows where each friend's side of the playing area is and they can only play with the blocks on their side of the line. This way, they don't argue anymore and can both have fun playing with their own blocks. Demarcation lines are used in other places too, like in sports games to show where the ball is out of bounds or in war to show where the two sides have agreed to stop fighting. So, a demarcation line is just a line drawn to show where something starts and ends.