The paper "What is a geomagnetic storm?" by W. D. Gonzalez et al. reviews the definition and characteristics of geomagnetic storms, focusing on their interplanetary and magnetospheric origins. The authors define a geomagnetic storm as an interval of time when a sufficiently intense and long-lasting interplanetary convection electric field leads to a substantial energization of the magnetosphere-ionosphere system, resulting in an intensified ring current that exceeds a key threshold of the storm time Dst index. The relationship between storms and substorms is also discussed, with basic mechanisms of this relationship presented and analyzed. The paper highlights the importance of understanding the physics behind this relationship and suggests recommendations for future improvements in monitoring geomagnetic indices and the solar wind near Earth. The authors review historical aspects of geomagnetic storm research, the role of the interplanetary medium in storm origins, and the seasonal and solar cycle distribution of storms. They also explore the storm/substorm relationship, questioning whether intense substorms are necessary for the development of a magnetic storm and discussing the efficiency of energy injection into the ring current. The paper concludes with a discussion on the physical processes controlling the efficiency of energy input into the ring current and the role of the interplanetary magnetic field (IMF) in regulating this process.The paper "What is a geomagnetic storm?" by W. D. Gonzalez et al. reviews the definition and characteristics of geomagnetic storms, focusing on their interplanetary and magnetospheric origins. The authors define a geomagnetic storm as an interval of time when a sufficiently intense and long-lasting interplanetary convection electric field leads to a substantial energization of the magnetosphere-ionosphere system, resulting in an intensified ring current that exceeds a key threshold of the storm time Dst index. The relationship between storms and substorms is also discussed, with basic mechanisms of this relationship presented and analyzed. The paper highlights the importance of understanding the physics behind this relationship and suggests recommendations for future improvements in monitoring geomagnetic indices and the solar wind near Earth. The authors review historical aspects of geomagnetic storm research, the role of the interplanetary medium in storm origins, and the seasonal and solar cycle distribution of storms. They also explore the storm/substorm relationship, questioning whether intense substorms are necessary for the development of a magnetic storm and discussing the efficiency of energy injection into the ring current. The paper concludes with a discussion on the physical processes controlling the efficiency of energy input into the ring current and the role of the interplanetary magnetic field (IMF) in regulating this process.