Lyman-alpha refers to a research area in astrophysics that focuses on studying the Lyman-alpha spectral line of hydrogen atoms. This spectral line is produced when an electron transitions from an excited state to the ground state in a hydrogen atom, emitting a photon with a specific wavelength in the ultraviolet region of the electromagnetic spectrum. Researchers study Lyman-alpha emission to understand a variety of astrophysical phenomena, such as the formation and evolution of galaxies, the intergalactic medium, and the reionization of the universe. Observations of Lyman-alpha emission can provide insights into the distribution of hydrogen gas, the properties of galaxies, and the conditions of the early universe. Overall, research in the field of Lyman-alpha plays a crucial role in advancing our understanding of the universe and its evolution over cosmic time.