Microflares and nanoflares in the solar corona

Due to the increase in the spatial and temporal resolution of observations of the solar atmosphere, which is mainly associated with progress in space research, we now understand that the Sun's activity not only is associated with large centers, but also extends to significantly smaller scales. Each new advance in experimental technology over the past 60 years has led to the discovery of more and more numerous and small solar structures: X-ray active regions in the 1960s, hot X-ray points in the 1970s, solar microflares in the 1980s, and finally, from the end of the 20th century, solar nanoflares. At the same time, the total energy release, obtainable from observations, is still insufficient to ensure a balance between heating of the corona and its rapid radiative cooling. For the smallest-scale phenomena, nanoflares, it is still not possible to resolve their structure and mechanism, which raises the question of whether it is correct to classify them as flares. We present a review of the main results obtained so far in the field of small-scale solar activity, mainly microflares and nanoflares, and discuss the main issues that need to be solved in order to move forward.