Who defines death ? There's no one definition of death.
If by death you mean departing from this world then both muslims and christians believe jesus has departed this world.
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Scripture defines death as separation. There is a physical death and a spiritual death. When the body dies the soul/spirit is separated from the body. Spiritual death or the second death is mans separation from Christ. A man without Christ is spiritually dead. We are given the Holy Spirit of God when when we place our faith in the death and resurrection of Christ for our sins. We then become spiritually alive. Christ died physically for our sins but three days later He raised from the dead. His physical body was rejoined with His spirit. Some theologians believe the only man made thing in heaven are the scars and wounds in His body.
Ephesians 2:1-10
1 And you He made alive, who were dead in trespasses and sins,
2 in which you once walked according to the course of this world, according to the prince of the power of the air, the spirit who now works in the sons of disobedience,
3 among whom also we all once conducted ourselves in the lusts of our flesh, fulfilling the desires of the flesh and of the mind, and were by nature children of wrath, just as the others.
4 But God, who is rich in mercy, because of His great love with which He loved us,
5 even when we were dead in trespasses, made us alive together with Christ (by grace you have been saved),
6 and raised us up together, and made us sit together in the heavenly places in Christ Jesus,
7 that in the ages to come He might show the exceeding riches of His grace in His kindness toward us in Christ Jesus.
8 For by grace you have been saved through faith, and that not of yourselves; it is the gift of God,
9 not of works, lest anyone should boast.
10 For we are His workmanship, created in Christ Jesus for good works, which God prepared beforehand that we should walk in them.