A small opening or hole that allows one to see through, often used for privacy or security.

झलक दिखाने वाला छिद्र

English Usage: She looked through the peep hole to see who was at the door.

Hindi Usage: उसने दरवाजे पर किसका चेहरा है यह देखने के लिए झलक दिखाने वाले छिद्र से देखा।