Easter or Easter Sunday is one of the prominent and oldest festivals of the Christian Church. The day signifies resurrection of the Jesus Christ. According to the Christian Greek Scriptures, New Testament (it is about the teachings and the persons of the Jesus and different events that took place in first century Christianity) on the third day of Jesus crucifixion, he rose again.
If scripture is to be believed than after the Romans crucified Jesus, his body was buried in new tomb, however, God raised him from the dead and he appeared to many people till he was taken in the heaven to sit next to the god. The day is the culmination of the Passion of Christ (account of Jesus visit to Jerusalem and his citification) proceeded by Lent (or Great Lent). The 40 days in which Jesus appeared to many people is considered as Lent.
Lent begins on Ash Wednesday and ends before Easter Sunday.