What is the meaning of Geomagnetic Storm?

The geomagnetic storm is caused by magnetic activity on the outermost portion of the sun. The Sun is always releasing a steady amount of charged particles into space. This is called solar wind. The solar wind also carries with it the solar magnetic field.

When particularly intense particle explosions occur on the Sun in a certain direction, the Earth occasionally gets into or strikes the path of the solar wind generated by this event, which is known as a geomagnetic storm OR a storm of solar winds emanating from the Sun spreads around the Sun, but when the Sun explodes, and when this explosion begins to accelerate together with the solar winds, it is called a magnetic storm. If this storm starts coming towards Earth, then this storm is called a geomagnetic storm.

A Magnetosphere is that area of space, around a planet,i.e. controlled by the planet's magnetic field. The shape of the earth's magnetosphere is the direct result of being blasted by the solar wind. The solar wind compresses its sunward side to a distance of only 6 to 10 times the radius of the earth. The solar wind drags out the night-side magnetosphere to possibly 1000 times Earth's radius; its exact length is not known. This extension of the magnetosphere is known as the Magnetotail. The outer boundary of Earth's confined geomagnetic field is called Magnetopause. The Earth's magnetosphere is a highly dynamic structure that responds dramatically to solar variations.

There are two main types of geomagnetic storms: recurrent and nonrecurrent storms. 

Recurrent storms are caused by features on the Sun called coronal holes that live for several months and generate corotating interaction regions (disturbances in the solar wind where the fast solar wind from the coronal holes catches up with the slow solar wind) that repeat on the 27-day solar rotation period. 

Nonrecurrent storms occur sporadically throughout the solar rotation but are primarily driven by CMEs. 

When solar wind hits the magnetosphere, it transfers mass, energy, and momentum into this layer. The magnetosphere can absorb most of the energy from the everyday level of solar wind. But during strong storms, it can get overloaded and transfer excess energy to the upper layers of Earth’s atmosphere near the poles. This redirection of energy to the poles is what results in fantastic aurora events, but it also causes changes in the upper atmosphere that can harm space assets. The significant increase in high-energy electrons within the magnetosphere during strong geomagnetic storms means more electrons will penetrate the shielding on a spacecraft and accumulate within its electronics. This buildup of electrons can discharge in what is basically a small lightning strike and damage electronics.

A Geomagnetic storm does not threaten humans, but it can affect satellites (or communicate satellites) orbiting the earth as well as GPS. it can also disrupt some radio communication and cause errors in any part of a spacecraft's electronics system. if the error occurs in something critical, the entire satellite can fail. Geomagnetic storms are brief disturbances in the earth's magnetic field and magnetic sphere caused by a burst of radiation and charged particles from the sun. the calibrations in place for a quiet atmosphere become wrong during geomagnetic storms.