The word shrove is a past tense of the English verb “shrive,” which means to obtain absolution for one’s sins by confessing and doing penance. Shrove Tuesday gets its name from the shriving (confessing) that English Christians were to do along with the imposition of penance and pronouncement of absolution that Christians were required to do prior to Ash Wednesday in order to be spiritually clean and prepared for the 40-day Lenten period. In English-speaking areas the Tuesday before Ash Wednesday is the equivalent of Carnival in latin European countries and was known as Shrove Tuesday. In latin counties it was known as Martes de Carnaval (Tuesday of Carnival) while German speakers called it Faschingsdienstag (Fat Tuesday).
The reason for pancakes on the day before Ash Wednesday is that the Lenten period of 40 days is associated with a liturgical fast or abstention from certain rich foods. Eggs, meat, milk, sugar, oil are not used during that period and are disposed of immediately prior to the time of fasting. Pancakes, cakes, doughnuts and sausages were efficient ways of using up those items with wouldn’t normally last through the 40 day fast.