The cessation of the bodily functions of a human being through the departure of the soul. It is part of revelation that, in the present order of divine providence, death is a punishment for sin. According to the teaching of the Church, death is a consequence of Adam's sin, as declared by St. Paul: "Sin entered the world through one man, and through sin death" (Romans 5:12). In the case of those justified by grace, death loses in penal character and becomes a mere consequence of sin. All human beings, therefore, are subject to death, although in the case of Christ and his Mother, because of their freedom from sin, death was neither a punishment for sin nor a consequence of sin. Yet, as they were truly human, death was natural for them.
Death is also the end of human probation or testing of one's loyalty to God. It ends all possibility of merit or demerit.
Properly speaking, only the body dies when separated from its principle of life, which is the soul. However, the Bible speaks of a second death (Revelation 20:6), referring to the souls in hell, who are separated from their principle of supernatural life, which is God.