The narrow-line region (NLR) is a region in the nucleus of active galaxies, such as Seyfert galaxies and quasars, where emission lines from ionized gas are observed with relatively narrow widths. This region is believed to be the result of the interaction between the ionizing radiation from the central supermassive black hole and the surrounding gas in the galaxy. The study of the NLR can provide valuable information about the physical and chemical properties of the gas in the vicinity of the black hole, as well as insights into the processes driving the activity and evolution of active galactic nuclei. Research in this area often involves spectroscopic observations and modeling of the emission lines to better understand the nature of the NLR and its connection to the overall structure and activity of galaxies.