Shrove Tuesday is the Tuesday before Ash Wednesday which is the first day of Lent. It’s a day of penitence, to clean the soul, and a day of celebration as the last chance to feast before Lent begins.
Lent is a time of abstinence, of giving things up. So Shrove Tuesday is the last chance to indulge yourself, and to use up the foods that aren’t allowed in Lent. Historically, in the old days there were many foods that Christians would not eat during Lent such as meat and fish, fats, eggs, and milky foods. So families wouldn’t be wasteful, they would have a feast on the shriving Tuesday, and eat up all the foods that would go bad over the next 40 days.
Pancakes became associated with Shrove Tuesday because they were a dish that could use up all the eggs, fats and milk in the house with just the addition of flour.