Alternate Definitions for flare

A sudden eruption of energy in the solar atmosphere lasting minutes to hours, from which radiation and particles are emitted. Flares are classified on the basis of area at the time of maximum brightness in H-alpha and on the peak flux of 1 minute averaged GOES XRS 0.1 – 0.8 nm band x-rays.  For x-ray flare classifications, see the definition for x-ray flare class.  The H-alpha classifications are given here..
Importance 0 (Subflare):
<= 2.0 hemispheric square degrees
Importance 1:
2.1-5.1 square degrees
Importance 2:
5.2-12.4 square degrees
Importance 3:
12.5-24.7 square degrees
Importance 4:

= 24.8 square degrees
[One square degree is equal to (1.214 x 104 km2) = 48.5 millionths of the visible solar hemisphere.] A brightness qualifier F, N, or B is generally appended to the importance character to indicate faint, normal, or brilliant (for example, 2B).

A flare is a violent explosion in the atmosphere of a star. Flares take place in the corona and chromosphere, heating plasma to tens of millions of kelvins and accelerating electrons, protons and heavier ions to near the speed of light. They produce electromagnetic radiation across the electromagnetic spectrum at all wavelengths from long-wave radio to the shortest wavelength gamma rays Most flares occur in active regions around sunspots, where intense magnetic fields emerge from the surface into the corona. Flares are powered by the sudden (timescales of minutes to tens of minutes) release of magnetic energy stored in the corona.