What Is Easter?

On Easter Sunday, Christians celebrate the resurrection of the Lord, Jesus Christ. It is typically the most well-attended Sunday service of the year for Christian churches.
Christians believe, according to Scripture, that Jesus came back to life, or was raised from the dead, three days after his death on the cross. As part of the Easter season, the death of Jesus Christ by crucifixion is commemorated on Good Friday, always the Friday just before Easter. Through his death, burial, and resurrection, Jesus paid the penalty for sin, thus purchasing for all who believe in him, eternal life in Christ Jesus.

When Is Easter Season?

Lent is a 40-day period of fasting, repentance, moderation and spiritual discipline in preparation for Easter. In Western Christianity, Ash Wednesday marks the start of Lent and the Easter season.

Easter Sunday marks the end of Lent and the Easter season.

Eastern Orthodox churches observe Lent or Great Lent, during the 6 weeks or 40 days preceding Palm Sunday with fasting continuing during the Holy Week of Easter. Lent for Eastern Orthodox churches begins on Monday and Ash Wednesday is not observed.
Because of Easter's pagan origins, and also because of the commercialization of Easter, many Christian churches choose to refer to the Easter holiday as Resurrection Day.

Easter in the Bible

The biblical account of Jesus' death on the cross, or crucifixion, his burial and his resurrection, or raising from the dead, can be found in the following passages of Scripture: Matthew 27:27-28:8; Mark 15:16-16:19; Luke 23:26-24:35; and John 19:16-20:30.
The word "Easter" does not appear in the Bible and no early church celebrations of Christ's resurrection are mentioned in Scripture. Easter, like Christmas, is a tradition that developed later in church history.

Determining the Date of Easter

In Western Christianity, Easter Sunday can fall anywhere between March 22 and April 25. Easter is a movable feast, always celebrated on the Sunday immediately following the Paschal Full Moon. I had previously, and somewhat erroneously stated, "Easter is always celebrated on the Sunday immediately following the first full moon after the vernal (spring) equinox." This statement was true prior to 325 AD; however, over the course of history (beginning in 325 AD with the Council of Nicea), the Western Church decided to established a more standardized system for determining the date of Easter. 
There are, in fact, as many misunderstandings about the calculation of Easter dates, as there are reasons for confusion.

Key Bible Verses About Easter

Matthew 12:40
For just as Jonah was three days and three nights in the belly of the great fish, so will the Son of Man be three days and three nights in the heart of the earth. (ESV)
1 Corinthians 15:3–8
For I delivered to you as of first importance what I also received: that Christ died for our sins in accordance with the Scriptures, that he was buried, that he was raised on the third day in accordance with the Scriptures, and that he appeared to Cephas, then to the twelve. Then he appeared to more than five hundred brothers at one time, most of whom are still alive, though some have fallen asleep. Then he appeared to James, then to all the apostles. Last of all, as to one untimely born, he appeared also to me. (ESV)