Shrove Tuesday gets its name from the ritual of shriving, when the faithful confessed their sins to the local priest and recieved forgiveness before the Lenten season began.
As far back as 1000 AD, "to shrive" meant to hear confessions. (Trivia note: the term survives today in the expression "short shrift" or giving little attention to anyone's explanations or excuses).
Historically, Shrove Tuesday also marked the beginning of the 40-day Lenten fasting period when the faithful were forbidden by the church to consume meat, butter, eggs or milk. However, if a family had a store of these foods they all would go bad by the time the fast ended on Easter Sunday. What to do?
Solution: use up the milk, butter and eggs no later than Shrove Tuesday. And so, with the addition of a little flour, the solution quickly presented itself in... pancakes. And lots of 'em.
Today, the Shrove Tuesday pancake tradition lives on throughout Western Europe, the United States, Canada and Australia, but is most associated with the UK where it is simply known as Pancake Day with a traditional recipe, although these can be as varied in the UK as there are British households.
In France, (as well as here in the US - or more famously - in New Orleans) it's known as Fat Tuesday which kicks off the Mardi Gras festival with wild celebrations just before the austere Lenten season.
In Sweden, Fat Tuesday translates to Fettisdagen, and in Lithuania it's Uzgavens. In Poland, traditional celebrations take place on a Thursday a week before Ash Wednesday and so it's Tlusty Czwartek, or Fat Thursday.