Sin simply means going against the commandments of God your creator and maker. The 10  Commandments were given by God to the children of isreal, through Moses, any persons that does contrary to these commandments have committed sin. In Romans 3:23 it says for all have sin and come short of the glory of God. So we are all sinners born in sin, from the very first man Adam , we all inherited sin. But Jesus gave 2 commandments, and it is when we fail to do as He has commanded that we have committed  sin. Sin is a great offense against God  and his Holy way of Living.