A character representing or associated with Lent in a festival pageant, mummers' play, etc. Also: an effigy of a man, typically made of straw and dressed in rags, paraded through the streets or set up as a target during Lent, and destroyed on Easter Day; (figurative and in figurative contexts) a target for criticism or ridicule. Now chiefly historical.
Sometimes representing Judas Iscariot.
Mid 16th century (in an earlier sense). From Jack + of + Lent.