Sin is any inclination to violate God, his character, or his desires. This includes our actions, attitudes, or nature.
The Bible clearly teaches that all people are sinful. Psalm 14:3 says: "All have turned aside, they have together become corrupt; there is no one who does good, not even one." Paul states this emphatically: "Jews and Gentiles alike are all under sin. As it is written: 'There is no one righteous, not even one'. . . . all have sinned and fall short of the glory of God." (Rom. 3:9-10, 23)