The Easter Season takes place from April 01 till May 20, 2018. Easter Season, or Eastertide, Paschal Time, Paschal Tide or Paschaltide, is a festal season in the liturgical year of Christianity. It is the period of fifty days from Easter Sunday to Pentecost Sunday.
The Easter Season is celebrated as a single joyful feast, indeed as the "great Lord's Day". Each Sunday of the season is treated as a Sunday of Easter, and, after the Sunday of the Resurrection, they are named Second Sunday of Easter, Third Sunday of Easter, etc. up to the Seventh Sunday of Easter, while the whole fifty-day period concludes with Pentecost Sunday.
Easter Sunday and Pentecost correspond to pre-existing Jewish feasts: The first day of Pesach and the holiday of Shavu'ot. In the Jewish tradition, the 49 days between these holidays are known as Counting of the Omer. (With material from: Wikipedia)