The new creation (Gk καινὴ κτίσις) is a concept found in the New Testament, related to the new life (ἐν καινότητι ζωῆς) and new man (referring to the spiritual rebirth through Christ Jesus) (καινός ἄνθρωπος) but with reference also to the Genesis "old creation."
In the letters of Paul
The language of a new creation is not limited to the two verses in the KJV that include that actual phrase (Gal. 6:15, 2 Cor 5:17). Other passages, such as Galatians 6:12-16, 2 Corinthians 5:14-19, Ephesians 2:11-22, Ephesians 4:17-24, and Colossians 3:1-11 present new creation teaching also, without that exact phrase.
Other references to the concept include the language Ephesians 2:10, "For we are his workmanship, created in Christ Jesus for good works, which God prepared beforehand, that we should walk in them." The old, Adamic creation could not be said to be in any sense "in Christ," so this must therefore be speaking of new creation.
Often the themes of the Genesis creation and new creation are contrasted, as, per N. T. Wright, in Colossians chapter 1, where the old creation and new creation in Christ (1:15-20) are compared with the new creation (vv. 21-23)