Holy Week is the most solemn and glorious week in Christianity, the pinnacle of the liturgical year. It's more sacred than Christmas! This is because Holy Week commemorates the final week of Our Lord's life, the very purpose for which Christmas happened.

Holy Week begins with Palm Sunday (when Jesus made his final entrance into Jerusalem) and culminates with Easter Sunday. As Holy Week progresses to its final days the solemnity heightens.
 

THE SACRED TRIDUUM

We strongly encourage you to participate in as much of the Sacred Triduum as possible.

Sundown on Holy Thursday to sundown on Easter Sunday is considered the most solemn part of the liturgical year. This three-day period is referred to as the Easter Triduum, also known as the Sacred Triduum, or Paschal Triduum.

Basically, the Sacred Triduum is one great festival recounting the last three days of Jesus' life on earth, the events of his Passion and Resurrection, when the Lamb of God laid down his life in atonement for our sins.

"Though chronologically three days, they are liturgically one day unfolding for us the unity of Christ's Paschal Mystery" (USCCB).

**Taken from https://www.catholiccompany.com/.../the-easter-triduum...