Spiral arms are long, thin regions of increased star formation and stellar density that occur in spiral galaxies. They are characterized by a winding structure that extends outward from the galaxy's central bulge. Spiral arms are thought to be the result of density waves traveling through the galactic disk, causing gas and dust particles to compress and ignite into new stars. These features are often visible in images of spiral galaxies and play a crucial role in shaping the overall structure and evolution of these galactic systems. Researchers study spiral arms to better understand the driving forces behind their formation and dynamics, as well as their impact on the evolution of galaxies over time.