XFEL is an acronym for X-ray free-electron laser, a powerful research tool used to study the molecular structure of everything from viruses to metals. However, there are other terms that can be used to refer to this technology. One such term is synchrotron radiation, which is produced by accelerating electrons and directing them into an undulating magnetic field. Another term is coherent radiation, which refers to the laser-like properties of the X-ray beam produced by an XFEL. Other possible synonyms include pulsed radiation, femtosecond laser, and ultrafast X-ray source. These terms may be used interchangeably, but they all refer to the same groundbreaking research tool that has revolutionized the study of materials science, biology, and chemistry.