Maslenitsa (also known as Butter Week, Pancake week or Cheesefare Week), is a Russian, Ukrainian and Belarusian religious and folk holiday. In 2012 it is celebrated from February 20 to February 26. Maslenitsa has its origins in both pagan and Christian traditions. In Slavic mythology, Maslenitsa is a sun festival, celebrating the imminent end of the winter.
Shrove Tuesday is a term used in English-speaking countries, especially the United Kingdom, Canada, Australia, New Zealand, and parts of the United States for the day preceding Ash Wednesday, the first day of the season of fasting and prayer called Lent. Source