Lent is a forty-day period leading up to Easter when many Catholics give up luxuries such as meat. Mercutio is imagining a rabbit pie that someone has prepared ahead of time to be eaten secretly during Lent. But the meat in the pie is not likely to last forty days and will become moldy (hoar) before it is eaten. The word "hoar" also means gray with age, generally referring to someone’s hair, thus linking the gray hair on the nurse’s and servant’s heads with the mold on the top of the Lenten pie.