Maslenitsa is a pagan festival which was popular even before Christianization of Kievan Rus'. It is symbolized the end of winter. Proto-Slavic Maslenitsa was celebrated in the beginning of spring, on the vernal equinox (now it is about the 20th of March) when frost was completely finished and warm was coming. Now the most common traditions during this festival are eating pancakes, a solemn burning of the stuffed figure of winter, storming a snow town and fistfights. Maslenitsa is celebrated during the week preceding the Lent which is also called Pancake Week.
Pancake (blin) looks like the Sun (it is round, warm and yellow) that is why it is a symbol of this festival. There were special rituals for each day of Pancake Week. However Sunday is the last and the most important day for celebration.
You can take part in outdoor festival devoted to Maslenitsa on the 1st of March in Mayakovsky Central Park (230, Michurina St.). The beginning is at 11 a.m. Free entry.