Literally the fruit of a plant; metaphorically the outcome, result, or product of a life, action, or relationship. In the NT karpos becomes a rich metaphor for spiritual life: what a person's union with Christ produces, what a tree's quality reveals about its root, what the Spirit's presence generates in character.
Jesus's parable of the vine (John 15) makes karpos the measure of spiritual health: 'I am the vine, you are the branches. Whoever abides in me... bears much fruit.' Fruit is not earned by effort but grown through connection — to bear fruit is to remain in Christ. The Galatians 5 'fruit of the Spirit' deliberately contrasts with 'works of the flesh': fruit grows organically from within a Spirit-transformed life; works can be produced by willpower alone. John the Baptist demanded 'fruit in keeping with repentance' — outward evidence of inner change.