character Arc: the changes, evolution, or degradation that happen to a character over the course of the story or series. This transformation takes fiction beyond a mere series of events. The arc will often be based on lessons learned and reveal changes in behaviors, views, beliefs, under- standing, and motivation.
In other words, the character arc is how different the hero is at the end of the story.
One of the best character arcs I've read is in the gospels, in the life of the apostles.
Simon Peter and his brother, Andrew, were fishermen. They would wake up early in the morning, get on their boat and fish until they caught a good amount of fish. Then they would come to the shore, dragging the nets and separate the fish. Simon would untangle the nets and stretch them on the beach, while his brother carried the fish to their homes. Probably, they would eat some of the fish and go to bed exhausted. Just to wake up the next morning and do it all over again.
One day Jesus came along and they left their nets to follow him. One minute, they saw a lame man walking, the next a blind man’s eyes were open. Bread multiplied, crowds followed them. They were now recognized and admired, as those who walked with Jesus.
Simon and Andrew went from a predictable life of nets and scales, to a thrilling life of signs and wonders, where no one could be sure what would happen the next day. Would they have to run from an angry mob if Jesus healed again during the Sabbath? Or would they witness a demon-posessed man being set free and a herd of swine drown into the sea?
By the time Jesus rises from the dead and commissions them to make disciples of the nations, we have a totally different Simon (now called Peter) and Andrew. They are now fisher of men. The book of Acts of the Apostles tells of they great deeds of these two, but I won't describe it all here, you'll have to read it for yourself.
Actually, reading the gospels will not only teach you about writing fiction, it has the potential of creating a personal character arc in your own life.