Here is the Wikipedia definition aimed at the Western Christian Denominations.
Lent, in most Christian denominations, is the forty-day liturgical season of fasting and prayer before Easter.[1] The forty days represent the time Jesus spent in the desert, where, according to the Bible, he endured temptation by Satan.[2] Different churches will calculate the forty days differently.
The purpose of Lent is the preparation of the believer—through prayer, penitence, almsgiving and self-denial—for the annual commemoration of the Death and Resurrection of Jesus, as celebrated during Holy Week, which recalls the events linked to the Passion of Christ and culminates in Easter, the celebration of the Resurrection of Jesus Christ.
In Western Christianity, Lent lasts from Ash Wednesday until Easter Saturday.[1] The six Sundays in Lent are not counted among the forty days because each Sunday represents a "mini-Easter", a celebration of Jesus' victory over sin and death.[2] In those churches which follow the Byzantine tradition (e.g. Eastern Orthodox and Eastern Catholics), the forty days of Lent are calculated differently (see Great Lent): the fast begins on Clean Monday, Sundays are included in the count, and it ends on the Friday before Palm Sunday. The days of Lazarus Saturday, Palm Sunday and Holy Week are considered a distinct period of fasting. For more detailed information about the Eastern Christian practice of Lent, see the article Great Lent.