Advent
The four Sundays of Advent before the Christmas season begins
Christmas
Includes Christmas Day, the Feast of the Holy Family, and the Feast of Epiphany
Ordinary Time I
The Sundays between Epiphany and Ash Wednesday
Lent
Includes Ash Wednesday, the five Sundays of Lent, and Passion (or palm) Sunday
Triduum
Includes Holy Thursday, Good Friday, and Holy Saturday
Pentecost
Occurs fifty days after Easter
Easter
Includes Easter Sunday, the second through seventh Sundays of Easter, and Pentecost Sunday
Ordinary Time II
The Sundays between Pentecost and the first Sunday of Advent