Shrove Tuesday is often known as Pancake Day. It is the day before Ash Wednesday, and marks the start of Lent. The term Shrove Tuesday comes from the word shrive, meaning "confess", because traditionally this was the time when people looked carefully at their behaviour over the year just gone and considered what sins they needed to confess and be forgiven. Because one way to repent was to give up some kinds of food for Lent, the idea was that any food that was forbidden in Lent would be used up on the day before, so as not to waste it. A simple way of doing that was to make pancakes.
But there is more to the tradition than that. Before it was converted into a Christian Holy Day, it was a pagan festival. The pagans worshipped the Sun and marked the arrival of spring with the festival of the Sun. Pancakes are a round yellow symbol of the Sun. Eating pancakes was seen as taking in some of the power of the Sun. Many festivals like this were taken over by Christians as pagans were converted to Christianity.