Which term describes a fictitious prose narrative of book length, typically with characters and action represented realistically?

The term that accurately describes a fictitious prose narrative of book length, typically featuring characters and actions presented in a realistic manner, is indeed a novel. Novels are extended works of fiction that delve deeply into character development, plot, and themes, often reflecting the complexities of real life and human nature.

In contrast, a novella is a shorter fictional work that usually focuses on a single plot or character arc but lacks the extensive development found in a novel. A short story is even shorter, typically focusing on a confined event or moment, and it doesn't offer the same level of character and narrative complexity. A poem, on the other hand, is a different genre altogether, focusing on expressive language and often using verse and rhythm, rather than prose narrative. This distinction underlines why "novel" is the most suitable choice for the description provided.