What is the liturgical year?

The liturgical year is the Church calendar although it is quite different from the calendar year. The church calendar begins on a different day than the civil year, but it still contains the same 12 months and 365 days.

The liturgical year begins with the first Sunday of Advent, typically the first Sunday after Thanksgiving, which introduces a season of four weeks or slightly less duration with the theme of expectation of the coming of Christ. During the first two weeks, the final coming of Christ as Lord is the focus of attention. During the final weeks of Advent, the emphasis shifts to the anticipation of the celebration of his Nativity on Christmas. Advent has four Sundays. Since the 10th century, the first Sunday has marked the beginning of the liturgical year in the Western Church.

From the book, Catholicism for Dummies by Trigilio and Brighenti