The tradition of Maslenitsa (also known as Shrovetide) dates back to pagan times, when Russian folk would bid farewell to winter and welcome spring. As with many ancient holidays, Maslenitsa (stress on the first syllable) has a dual ancestry: pagan and Christian. On the pagan side, Maslenitsa was celebrated on the vernal equinox. It welcomed spring and was all about nature's rejuvenation and the bounty of sunny warmth. On the Christian side, Maslenitsa was the last week before the onset of Lent, giving one last chance to bask in worldly delights.
This week, meat may be forbidden, but believers are welcome to eat all the butter and cheese they like. Many Moscow restaurants have special pancake menus.