大斋期，亦称大斋节、大斋节期，天主教会称四旬期（旧称严斋期、封斋期），信义宗称预苦期，是基督教教会年历一个节期。英文写作Lent，意即春天。拉丁教会称Quadragesima，意即四十天（四旬）。整个节期从大斋首日（圣灰星期三/涂灰日）开始至复活节前日止，一共四十天（不计六个主日）。天主教徒以斋戒、施舍、克己及刻苦等方式补赎自己的罪恶，准备庆祝耶稣基督的由死刑复活的「逾越奥迹」。此期间特别以守斋（拉丁语：Ieiunium，禁食）为做复活节的准备，故从前称之为「严斋月」；但在中古前期，四旬期是为一般人成为基督徒及加入教会的预备期，后来才转变成大家所熟悉的做补赎、悔改以预备迎接基督复活的功能。

Lent (Latin: Quadragesima: Fortieth) is a solemn religious observance in the liturgical calendar that begins on Ash Wednesday and ends approximately six weeks later, before Easter Sunday. The purpose of Lent is the preparation of the believer through prayer, penance, repentance of sins, almsgiving, atonement, and self-denial. This event is observed by Christians in the Anglican, Eastern Orthodox, Lutheran, Methodist, and Roman Catholic Churches. Some Anabaptist and evangelical churches also observe the Lenten season. Its institutional purpose is heightened in the annual commemoration of Holy Week, marking the death, burial, and resurrection of Jesus, which recalls the tradition and events of the New Testament beginning on Friday of Sorrows, further climaxing on Jesus' crucifixion on Good Friday, which ultimately culminates in the joyful celebration on Easter Sunday of the Resurrection of Jesus Christ.