A key theme in the Gospel of Luke as well as in the preaching of John the Baptist, not to mention Jesus.
Metanoia is usually translated as either repentance or conversion. It comes from the Greek meta which means (among other things) to change, and noia which means thoughts. Literally, to change your mind. The New Testament usage of this word use always implies an about-face, changing the way one lives. Repentance is often more focused on the past – sorrow for what one did wrong. Metanoia is more about the future – doing things differently. Metanoia is about transformation.