Sin simply means missing the mark, and in so doing, not sharing in the prize (according to Strong's definition NT:264).
"...for all have sinned and fall short of the glory of God.." (Rom 3:23, NIV)
Falling short of God's glory - His standard or mark of righteousness and holiness.
Sin is lawlessness (1 John 3:4) or transgression of God's will, either by omitting to do what God's law requires or by doing what it forbids.
The transgression can occur in thought (1 John 3:15), word (Matt 5:22), or deed (Rom 1:32).
Mankind was created without sin, morally upright and inclined to do good (Eccl 7:29).
But sin entered into mankind when Adam and Eve disobeyed God by eating the forbidden fruit in the Garden of Eden (Gen 3:6).
Being the head of the whole human race, Adam's sin affected all future generations (Rom 5:12-21). His fallen nature was passed on to all his descendants. Out of this, man committed all kinds of sins (Matt 15:19); and no one is free from sin (Rom 3:23).
by: Joshua Ong