A sudden outbreak, outburst or eruption (originally of flame, but now used more generally of any violent activity or emotion). / A sudden intensification in activity.

plural of flare-up

(intransitive) To burn brightly again. / (intransitive) To become more intense suddenly. / (intransitive, sometimes with “out” instead of “up”) To burst out suddenly, as in anger.

present participle of flare up

simple past tense and past participle of flare up

Third-person singular simple present indicative form of flare up