All Christians sin, but all Christians are told to avoid sinning. How does the Bible define what sin is?

The power of sin is the law. Sin is the breaking of divine law.

1 Cor 15:

56 Now the sting of death is sin: and the power of sin is the law.

James 2:9 . . .YOU are working a sin, for YOU are reproved by the law as transgressors.

Romans 7:7 What, then, shall we say? Is the Law sin? Never may that become so! Really I would not have come to know sin if it had not been for the Law; and, for example, I would not have known covetousness if the Law had not said: "You must not covet."

All sin is lawlessness (1 John 3:4). And, though we are no longer under the law covenant, we are still under the command to love one another (Romans 6:14; John 13:34, 35; 15:17). Read 1 Corinthians 13 verses 4 through 7. If you truly love, than you will carry on no sin. And, though our love is imperfect, we still have God's undeserved kindness and the blood of our Lord, Jesus Christ, which allows us forgiveness of our sins. We must do our best not to sin. Otherwise, are we really under love's guidance?

The end of Romans 13 or 14 says that anything that does not come from faith is sin. Clearly, as Galatians 5:20-23 says, anything that is evil or wrong is obvious and should be regarded as sin. Read these passages and get in to the Word of God and get this stuff clarified for yourself. Its all for you.

As a Bisexual Christian, I totally agree.

Romans 3

27 Where, then, is boasting? It is excluded. Because of what law? The law that requires works? No, because of the law that requires faith. 28 For we maintain that a person is justified by faith apart from the works of the law. 29 Or is God the God of Jews only? Is he not the God of Gentiles too? Yes, of Gentiles too, 30 since there is only one God, who will justify the circumcised by faith and the uncircumcised through that same faith. 31 Do we, then, nullify the law by this faith? Not at all! Rather, we uphold the law.

The bible says that whatever is not faith is sin. I faith in Christ.

Sin: Preposterous concept invented by Bronze Age desert dwelling men to keep the sheep in line through fear and intimidation.

In regards to your questions, does it really matter what the definition is?

We are Christians, but we are also only human, and so, we Christians cannot possibly keep from sinning perfectly.

The whole reason people convert to Christianity is to be forgiven for their sin, it is not so that they will be perfect from here on out, for we already know, that is not possible.

But if it helps you, here is the best definition for sin that I have ever heard:

"Take this rule: whatever weakens your reason, impairs the tenderness of your conscience, obscures your sense of God, or takes off your relish of spiritual things; in short, whatever increases the strength and authority of your body over your mind, that thing is sin to you, however innocent it may be in itself."

-- Susanna Wesley (Letter, June 8, 1725)

Hope that helps.

Sin is the knowingly and willfully disobeying God.

SIN IS MISSING THE MARK.