the time, esp. the Tuesday (: cf. Mardi Gras), just before Ash Wednesday: so called from the custom of preparing for Lent by sacramental confession esp. during this period
See Shrovetide in American Heritage Dictionary 4
(shrōvˈtīdˌ)
noun
The three days, Shrove Sunday, Shrove Monday, and Shrove Tuesday, preceding Ash Wednesday.