“Saint” simply means “holy” (from the Latin sanctus). You could think of saints simply as each and every person you know who has been made better by knowing God. Or you could think of saints as heroes in heaven who have defied death through God’s power and now live forever to miraculously aid us still on earth. The extraordinary thing about the traditional Christian faith is that these two things are not that far apart—only time, God’s grace, and the minor matter of passing through death separate the two.
In the Catholic church, the title of saint is usually reserved for those Christians currently in heaven whose earthly lives can inspire us to love and follow God better.