Pascha is not counted simply as one feast among the Twelve Great Feasts. It stands at the center of the liturgical year as the celebration of Christ's Resurrection. The Twelve Great Feasts are major celebrations universally kept in Orthodox liturgical life.
Fixed and movable feasts
Some feasts have fixed dates, such as Nativity and Theophany. Others are connected to Pascha and move from year to year, such as the Entry of the Lord into Jerusalem, Ascension, and Pentecost.
The Twelve Great Feasts
The commonly listed Twelve Great Feasts are the Nativity of the Theotokos, Exaltation of the Cross, Entrance of the Theotokos into the Temple, Nativity of Christ, Theophany, Meeting of the Lord, Annunciation, Entry into Jerusalem, Ascension, Pentecost, Transfiguration, and Dormition of the Theotokos.
Why feasts matter
Feasts are not religious decoration. They teach the faithful to receive the events of salvation as present in worship, prayer, fasting, hymnography, icons, and parish life.
Calendar dates can differ between Orthodox jurisdictions that follow different calendars. Always check your local parish calendar.