“X-class” denotes the most intense flares, while the number provides more information about its strength. An X2 is twice as intense as an X1, an X3 is three times as intense, and on. An X-class flare of this intensity can cause degradation or blackouts of radio communications for about an hour.
Solar flares are powerful bursts of radiation. Harmful radiation from a flare cannot pass through Earth’s atmosphere to physically affect humans on the ground, however — when intense enough — they can disturb the atmosphere in the layer where GPS and communications signals travel. This can disrupt radio signals for anywhere from minutes to hours.
This flare did not have an associated Earth-directed coronal mass ejection (CME), another solar phenomenon that can send solar particles into space and affect electronic systems in satellites and on Earth.