  Flares, sometimes accompanied by coronal mass ejections (CMEs), are the
result of sudden changes in the magnetic field of stars with high energy
release through magnetic reconnection, which can be observed across a wide
range of the electromagnetic spectrum from radio waves to the optical range to
X-rays. In our observational review, we attempt to collect some fundamental new
results, which can largely be linked to the Big data era that has arrived due
to the expansion of space photometric observations of the last two decades. We
list the different types of stars showing flare activity, their observation
strategies, and discuss how their main stellar properties relate to the
characteristics of the flares (or even CMEs) they emit. Our goal is to focus,
without claiming to be complete, on those results that may in one way or
another challenge the "standard" flare model based on the solar paradigm.
