What is Lent? Historically, Lent is the 40-day period before Easter, which the Church uses to prepare for the celebration of our Lord Jesus Christ’s Resurrection on Easter Sunday.
Are acts of repentance appropriate on other days during Lent? Yes. Thus the Code of Canon Law states: "All Fridays through the year and the time of Lent are penitential days and time throughout the universal Church" (CIC 1250).
Why is Lent forty days long? Because 40 days is a traditional number of discipline, devotion, and preparation in the Bible. Moses stayed on the Mountain of God 40 days (Ex 24:18, 34:28), Elijah traveled 40 days before he reached the cave where he had his vision (1 Kings 19:8), Nineveh was given 40 days to repent (Jon 3:4), and most importantly, prior to undertaking his ministry, Jesus spent 40 days in the wilderness praying and fasting (Matt 4:2). Since Lent if a period of prayer and fasting, it is fitting for Christians to imitate their Lord with a 40-day period. Christ used a 40-day period of prayer and fasting to prepare for his ministry, which culminated in his death and resurrection, and thus it is fitting for Christians to imitate him with a 40-day period of prayer and fasting to prepare for the celebration of his ministry's climax, Good Friday (His crucifixion) and Easter Sunday (His Resurrection). Thus the Catechism of the Catholic Church states: "'For we have not a high priest who is unable to sympathize with our weaknesses, but one who in every respect has been tested as we are, yet without sinning' [Heb 4:15]. By the solemn forty days of Lent the Church unites herself each year to the mystery of Jesus in the desert." (CCC 540).
Why are the forty days called Lent? They are called Lent because that is the Old English word for spring. Not just because it is the season of the year during which it falls, but because Lent is the Church’s Springtime during which we start fresh. This is something unique to English. In almost all other languages, Lent’s name is a derivative of the Latin term, Quadragesima, or "the forty days.
What are appropriate activities for ordinary days during Lent? Giving up something we enjoy for Lent, doing physical or spiritual acts of mercy for others, prayer, fasting and abstinence, attention to our duties, and going to confession and other acts expressing repentance in general.
Why are acts of repentance appropriate at this time of year? Because it is the time leading up to the commemoration of Our Lord's death for our sins and the commemoration of his resurrection for our salvation. It is thus especially appropriate to mourn the sins for which he died. Humans have an innate psychological need to mourn tragedies, and our sins are tragedies of the greatest sort. Due to our fallen nature, humans also have a need to have set times in which to engage in behavior (which is why we have Sundays as a set time to rest and worship, since we would otherwise be likely to forget to devote sufficient time to rest and worship), it is appropriate to have set times of repentance. Lent is one of those set times
Why is giving up something for Lent such a good and beneficial custom? By denying ourselves something we enjoy, we discipline our wills so that we are not slaves to our pleasures. Just as indulging the pleasure of eating leads to physical flabbiness and, if this is great enough, an inability to perform in physically demanding situations, indulging in pleasure in general leads to spiritual flabbiness and, if this is great enough, an inability to perform in spiritual demanding situations, we when the demands of morality require us to sacrifice something pleasurable (such as sex before marriage or not within the confines of marriage) or endure hardship (such as being scorned or persecuted for the faith). By disciplining the will to refuse pleasures when they are not sinful, a habit is developed which allows the will to refuse pleasures when they are sinful. There are few better ways to keep one's priorities straight than by periodically denying ourselves things of lesser priority to show us that they are not necessary and focus our attention on what is necessary.
Is there such a thing as denying ourselves too many pleasures? Most definitely. First, God made human life contingent on certain goods, such as food, and to refuse to enjoy enough of them has harmful consequences. For example, if we do not eat enough food it can cause physical damage or (in the extreme, even death). Just as there is a balance between eating too much food and not eating enough food, there is a balance involved in other goods. Second, if we do not strike the right balance and deny ourselves goods God meant us to have then it can generate resentment toward God, which is a spiritual sin just as much as those of engaging in excesses of good things. Thus one can be led into sin either by excess or by defect in the enjoyment of good things. Third, it can decrease our effectiveness in ministering to others. Fourth, it can deprive us of the goods God gave us in order that we might praise him. Fifth, it constitutes the sin of ingratitude by refusing to enjoy the things God wanted us to have because he loves us. If a child refused every gift his parent gave him, it would displease the parent, and if we refuse gifts God has given us, it displeases God because he loves us and wants us to have them.
Aside from Ash Wednesday, which begins Lent, what are its principal events? There are a variety of saints' days which fall during Lent, and some of these change from year to year since the dates of Lent itself change based on when Easter falls. However, the Sundays during the Lenten season commemorate special events in the life of Our Lord, such as his Transfiguration and his Triumphal Entrance into Jerusalem on Palm Sunday, which begins Holy Week. Holy Week climaxes with Holy Thursday, on which Christ celebrated the first Mass, Good Friday, on which he was Crucified, and Holy Saturday -- the last day of Lent -- during which Our Lord lay in the Tomb before his Resurrection on Easter Sunday, the first day after Lent.