The Paschal Triduum
Within Holy Week is the Paschal Triduum.
The Paschal Triduum consists of the last three days of Holy Week – Holy Thursday, Good Friday and Holy Saturday. The USCCB calls it “the summit of the liturgical year”. Although it is composed of three days it is commemorated liturgically as one day.
A handy reference for the Triduum can be found at: United States Conference of Catholic Bishops Eighteen Questions on the Paschal Triduum: http://www.usccb.org/prayer-and-worship/liturgical-year/triduum/questions-and-answers.cfm