I'm not religious so to me there really is no such thing as a "sin". However I guess it would be something very similar to "morally wrong/unacceptable"
I feel like anything that is against the universal law such as stealing , killing and lying. The 10 commandants defines the true definition of sin.
In my humble opinion, I believe that a sin is an act that you commint which is morally wrong, and you commit despite the fact you know that it is wrong.
For me, a sin is an act of disobedience to your religion, to your country's laws and to your principles. A sin is something that makes you doubt, it goes against your conscience. There are some people who commit heinous crimes and though some say these people don't have conscience. I believe otherwise, their conscience is still there, bugging them when they're alone.
Sin is not fluid. Sin in a Biblical sense is not fluid. It is as it was. You either choose to ignore that it is sin. You don't view it as a sin, but to people who believe in Abrahamic religions they still perceive it as a sin.
I'm a firm believer of the Golden Rule of "Do not impose on others what you do not wish for yourself." And my understanding of sin is in conformation with that belief. For example, I don't want somebody murdering me or my family, and I would not do that to another person or their family. So to me murder is a sin. To me, it is just the most logical mode of thought and action.
I wоuld dеfinе sin аs thоsе things (bе thеy асtiоns, stаtеs оf mind оr sо оn) thаt аrе соntrаry tо thе nаturе оf Gоd, аnd thеrеfоrе distаnсе thе individuаl whо аdоpts оr соmmits thеm frоm Gоd. This соuld tаkе thе fоrm оf dаmаging thе pеrsоnаl rеlаtiоnship bеtwееn thе individuаl аnd Gоd, subduing thе wоrk оf thе Hоly Spirit within thе individuаl, hаlting оr rеvеrsing thе prосеss оf thеоsis undеrwаy in thе pеrsоn... prоbаbly аll оf thоsе things аs wеll аs inеxprеssiblе оthеrs. Thеy аrе thоsе things thаt lеаd thе spirit аwаy frоm Gоd, whо is lifе аnd lоvе, аnd thеrеfоrе tоwаrds dеаth, spitе, misеry аnd оthеr suсh undеsirаblе stаtеs.
An action, consciously done, with the intent to hurt others or elevate oneself through unjust means. That for me is the ultimate meaning of sin. Habitually taking advantage of others and discarding your conscience, you become a sinner through and through.
Sin is an action or a thought against some moral standards. Everything we do that is against these standards can be classified as a sin and in Bible we have deadly sins that are basically the general guidance for us to become decent people on a basic level. Do not kill. Do not steal, etc. After these we have small sins that we need to recognize and avoid if possible.
I think that it is really one of those areas that can be hard to define and put into words. I cannot remember who said it or what they were talking about, but it goes something like this: I don't know how to describe it, but I know it when I see it. I think that you could put sin into that category, at least that is the way I feel about it.