The Catechism in Questions & Answers

532. What is death?

There is a distinction between the physical death and the spiritual death of a human being. Physical death signifies the end of life on earth. When it occurs, soul and spirit leave the body. Spiritual death is the separation of a human being from God. It is the consequence of sin.
When the Bible speaks of the “second death” (cf. Revelation 20: 6; 21: 8), this refers to the separation from God that takes effect after the Last Judgement.

Last Judgement: see Questions 579. et seq.

“For the wages of sin is death, but the gift of God is eternal life in Christ Jesus our Lord.”
Romans 6: 23