A division or dividing line. For example, curtains in a window divide the inner world and the outer world. A curtain on a stage divides the real world (audience) from the pretend world (stage). A curtain in a hospital room divides one patient's space from the next one.
Privacy, protection, or personal boundaries. For example, a house with no curtains could mean you're feeling emotionally exposed or vulnerable somehow, or as if other people have too much say in your life right now.
Opening your curtains could represent a mental or emotional openness to others or the world.
Closing your curtains could represent: