Christus vivit ('Christ is Alive') is a post-synodal apostolic exhortation of Pope Francis, written in response to the Fifteenth Ordinary General Assembly of the Synod of Bishops, on young people, faith and vocational discernment, held from 3 to 28 October 2018. It is addressed "to young people and to the entire people of God".
An apostolic exhortation is a magisterial document written by the pope.
It's essentially a pastoral message the pope sends out to Catholics to highlight key points about a particular issue. An apostolic exhortation establishes a clear direction for Catholics to critically address issues that are being discussed within the Church and in modern society.