In the Bible, a saint is a genuinely saved person. When a person repents and believes in the Lord Jesus Christ, that person becomes a new creature in Christ, he at that moment becomes a 'saint.' The word 'saint' means 'holy' or 'separated ones.' It is a classification designated for all the people of God. At salvation God separates us from sin, the world, our flesh, the Devil. And God draws us unto Himself. Therefore 'sainthood' is not a long formal process of canonizing a person, rather, a saint is anyone whom the Lord has cleansed or saved. Jesus imputes His righteousness upon us, and that makes us 'holy ones.' Our holiness does not extend from ourselves. In fact, we have no righteousness at all. Unless God does the saving we are lost sinners, bound to an eternal Hell.
The Bible informs us that we are saints 'in Christ.' This speaks of the close relationship we share as being God's people. First, we are not saints because of what we do, or who we are. Rather 'in Christ' we become saints. Secondly, the idea I believe that the phrase 'in Christ' is trying to convey is that believers have a unity, or a oneness with their Lord and Saviour Jesus Christ. Ephesians chapter 1 deals with this phrase a lot. Perhaps you could take some time to enumerate from that chapter the many glorious descriptions of being 'in Christ' or 'in Him.'
So who are the saints in Christ? They are the saved people of God. It is not an merely an elite group, rather it is a group of regenerated folks. This also should serve as a reminder to us of who we really are in Christ. The Bible declares us (i.e. you and me - if you are saved) to be saints. And so we can and should live holy lives. We should live out what we really are. As light is different from darkness, so should every saint live differently from those who are not saved. And just like every believer is a 'servant' (slave) to Jesus Christ, so it is that every believer is a 'saint in Christ Jesus.' The only way you can avoid being a servant and or a saint is to not be genuinely saved.
What a blessing! as genuine believers, we are both servants and saints.