This is the third in a series of essays on terms used in solar-terrestrial physics that are thought to be in need of clarification. Terms are identified and essays are commissioned by a committee chartered by Division II (Sun and Heliosphere) of the International Astronomical Union. Terminology Committee members include Ed Oliver (chair), Jean-Louis Bougeret, Hilary Cane, Takeo Kosugi, Sara Martin, Rainer Schwenn, Lidia van Driel-Gestelyi, and Joe Borovsky.

Writers are asked to review the origins of a term and its current usage/misusage. The main point is to open a discussion and inform the community. We solicit letters to Eos on the following article by Ioannis Daglis on the term “magnetic storm,” which is certainly one of the most venerable names in solar-terrestrial physics. In addition, we welcome suggestions to any committee member on other terms to address in this forum.