The word Bildungsroman is German in origin, made up of the words bildung, which means formation or education, and roman, which means novel. Thus, a Bildungsroman is a story that details the formation of the protagonist's character and identity. The main character is often introduced as a child (or, at least, someone who is relatively immature compared to a typical adult). This character has experiences which influence and affect them, likely resulting in some kind of personal crisis. Finally, they overcome or respond to the crisis in such a way that their identity and maturity develop, and they take their place within the world.
Alienation from one's society or family is a common theme in these stories, as this can easily produce crises of confidence to which the protagonist must respond. Class structure and poverty are also common themes for the same reason. Unrequited love or sexual frustration can also produce these effects.