The last day before Lent WordNet 3.0 & Open English WordNet

Shrove Tuesday or Pancake Day is the day before Ash Wednesday, observed in many Christian countries through participating in confession and absolution, the ritual burning of the previous year's Holy Week palms, finalizing one's Lenten sacrifice, as well as eating pancakes and other sweets. Wikipedia

Day in February or March preceding Ash Wednesday Wikidata

The last day of a carnival, traditionally the celebration immediately before the start of Lent when joy would be out of place for Christians. Wiktionary

The day before the beginning of Lent, when pancakes are traditionally eaten, originally to use up milk and eggs that would otherwise spoil because of not being eaten during Lent. Wiktionary

Day before the beginning of Lent. Wiktionary (translation)