fel

Fel is a short word with several distinct uses in different languages and disciplines. It can indicate a scientific acronym, function as a common word in European languages, or serve as a personal name. Because of this diversity, its meaning must be inferred from context.

Free Electron Laser (FEL) is a type of laser that generates coherent electromagnetic radiation by passing a beam of relativistic electrons through a periodic magnetic structure called an undulator. It does not rely on atomic transitions, is tunable across a wide wavelength range, and can reach X-ray energies. Prominent facilities include the Linac Coherent Light Source (LCLS) at SLAC and FLASH at DESY.

In Hungarian, fel is a directional particle or prefix meaning "up" or "on." It combines with verbs to indicate upward movement or the completion of an action, and often forms separable phrasal verbs such as felkel (to rise/get up) or felépít (to build up).

In Dutch, fel is an adjective meaning "bright" or "intense." It describes colors, light, or feelings and is used in compounds such as felgroen (bright green) or fel licht (bright light).

In Swedish, fel means "wrong" or "error" and is used to label mistakes or incorrect results, as in Det blev fel ("That went wrong") or ett fel ("an error").

As a personal name, Fel can be a given name or a shortened form of Felix in various languages.