The broad line region (BLR) is a region of ionized gas surrounding a supermassive black hole in the center of active galactic nuclei (AGN). The BLR emits broad spectral lines that are believed to originate from the high-speed motion of gas clouds that are orbiting close to the black hole. Studying the BLR is important for understanding the physics of AGN, as well as the role of black holes in galaxy evolution. Researchers use techniques such as spectroscopy to analyze the properties of the broad lines and deduce information about the structure and dynamics of the BLR.