A stellar flare is the release of a large amount of energy from a star. It occurs around sunspots and is powered by magnetic energy that's stored in a star's corona. A colossal coronal mass ejection releases clouds of electrons, ions, and atoms through the corona of a star into space. It produces radiation across the electromagnetic spectrum and all wavelengths from radio waves to gamma rays. Many stellar flares are invisible to the naked eye. It can disrupt radio communications.
The frequency of stellar flares depends on the star cycle. It can be several times a day or a few times per week.
It's called a solar flare when it happens on Sol.