Death

Spiritual death - Separation / alienation of soul from God
Physical death - Separation of soul from body
Eternal death - Spiritual death made permanent

Men are born spiritual dead. Both believers and unbelievers proceed to physical death. Believers are born again (John 3:5). They will not see eternal death (Revelations 20:6). Unbelievers will proceed to eternal death (Revelation 20:14).

Spiritual Death
One of the most complete descriptions of our conditions before we become believers - we were spiritually dead.

Ephesians 2:1-3 (HCSB)
And you were dead in your trespasses and sins in which you previously walked according to this worldly age, according to the ruler of the atmospheric domain, the spirit now working in the disobedient. We too all previously lived among them in our fleshly desires, carrying out the inclinations of our flesh and thoughts, and by nature we were children under wrath, as the others were also.

Physical death
Body goes to the dust (Ecclesiastes 12:7) and soul to Sheol.
Ecclesiastes 12:7 KJV
Then shall the dust return to the earth as it was: and the spirit shall return unto God who gave it.
James 2:26 KJV
For as the body without the spirit is dead …
Hebrews 9:27 ESV
And just as it is appointed for man to die once, and after that comes judgment,

World’s view of physical death - funeral and mouners
Ecclesiastes 12:5 NASB
For man goes to his eternal home while mourners go about in the street.

Eternal death
Isaiah 66:24 ESV
For their worm shall not die, their fire shall not be quenched, and they shall be an abhorrence to all flesh.
Revelation 20:14 ESV
Then Death and Hades were thrown into the lake of fire. This is the second death, the lake of fire.

Death is the result of sin
Ezekiel 18:4 ESV
Behold, all souls are mine; the soul of the father as well as the soul of the son is mine: the soul who sins shall die.
Romans 5:12 KJV
Wherefore, as by one man sin entered into the world, and death by sin; and so death passed upon all men, for that all have sinned:
Romans 5:17 ESV
For if, because of one man’s trespass, death reigned through that one man, much more will those who receive the abundance of grace and the free gift of righteousness reign in life through the one man Jesus Christ.
Romans 6:23 KJV
For the wages of sin is death; but the gift of God is eternal life through Jesus Christ our Lord.
1 Corinthians 15:22 ESV
For as in Adam all die, so also in Christ shall all be made alive.
1 Corinthians 15:56 ESV
The sting of death is sin, and the power of sin is the law.
James 1:15 KJV
Then when lust hath conceived, it bringeth forth sin: and sin, when it is finished, bringeth forth death.

Death, the Last Enemy
1 Corinthians 15:24-26 ESV
Then comes the end, when he delivers the kingdom to God the Father after destroying every rule and every authority and power. For he must reign until he has put all his enemies under his feet. The last enemy to be destroyed is death.
Revelation 21:4 ESV
He will wipe away every tear from their eyes, and death shall be no more, neither shall there be mourning, nor crying, nor pain anymore, for the former things have passed away.