Google dictionary says justification means the action of declaring or making righteous in the sight of God. This is close to what the Bible says. The Biblical meaning is the act of God declaring a sinner righteous through faith in Jesus Christ, rather than by works of the law. (Galatians 2:16). The difference between the two definitions is that only God can justify us through Jesus Christ, our Lord. (Romans 4:5). Because Jesus died for our sins, we appear clean in the sight of God. (Romans 5:1-2). 

I have heard the phrase “Just - if - I  never sinned." (1 John 1:9). 2 Corinthians 5:17 tells us that we become a new creation (Sinless) and the old (sinful) way of life is now gone. Just because God forgives us of our sins through Jesus does not mean we can keep on sinning. (Romans 6:1-2)

For more information, the Apostle Paul talks about sin in Romans chapters 7 & 8. 

Galatians 2:16, know that a person is not justified by the works of the law, but by faith in Jesus Christ. So we, too, have put our faith in Christ Jesus that we may be justified by faith in Christ and not by the works of the law, because by the works of the law no one will be justified.

Romans 4:5, However, to the one who does not work but trusts God who justifies the ungodly, their faith is credited as righteousness.

Romans 5:1-2, Therefore, since we have been justified through faith, we have peace with God through our Lord Jesus Christ, 2through whom we have gained access by faith into this grace in which we now stand. And we boast in the hope of the glory of God. 

1 John 1:9, If we confess our sins, he is faithful and just and will forgive us our sins and purify us from all unrighteousness.

2 Corinthians 5:17, Therefore, if anyone is in Christ, the new creation has come: The old has gone, the new is here!

Romans 6:1-2, What shall we say, then? Shall we go on sinning so that grace may increase? 2By no means! We are those who have died to sin; how can we live in it any longer?