A remnant is an object, thing, person, or group that survives an event, catastrophe, pruning, etc.  It is what is leftover.  In the Bible, the idea of a remnant deals mainly with the believers.  But remnant is also used in other ways, such as a remnant of a name (2 Samuel 14:7), of the Amorites (2 Sam 21:2), of the house of Judah (2 Kings 19:30), of inheritance (2 Kings 21:14 ), and of the saved (Rom. 9:27; 11:5).

God retains for himself those who are his people.  Many religious groups believe themselves to be the remnant of God’s true followers.  Mormons, Jehovah’s Witnesses, etc., claim to be what is left over after the falling away of the world into sin and apostasy.  However, the true remnant is those who are the elect of God (Matthew 24:24; Ephesians 1:4-5).  They are the ones whom God has called to himself and to our redeemed.