Shrove Tuesday, ca. 1200 meant three things: food, cockfighting, and mummers.
Food, obviously. A forty-day fast was about to begin. Chiefly, they would eat no animal products, so any and all animal products, especially meat, had to be eaten. The pre-fast feast came to last three days. By the end of the medieval period, it had developed its French name, Mardi Gras; it was the Carnival because they ate meat (cf chili con carne).
Schoolboys made it the season to hold cockfights. Medieval people didn’t think cockfights were cruel; roosters were the knights of the bird world, and they were merely letting the knights hold a feathered tournament.
In Germany and England, but especially in England, they put on mumming plays. We talked about mumming at Christmas; this was the other season, when the death and rebirth of the Turk (or Wild Man, or other) probably had pagan seasonal symbolism for spring. German/English mumming and Mardi Gras perhaps blended during the Renaissance to create the masked revel traditions of the Latin world today. (that last bit is a guess.)