What term describes the characters, places, and events that originate in the author's mind?

The term that best describes characters, places, and events that originate in the author's mind is "fictional." Fictional elements are those that are not based on real-life experiences or factual occurrences but rather are products of creativity and imagination. When an author creates a story, they build a world with characters and events that may reflect certain aspects of reality but are ultimately invented.

"Imaginary" could be considered a reasonable term in a more general sense, as it implies that the elements do not exist in reality; however, "fictional" specifically denotes invented narratives and constructs within literature. The choice "creative" refers more broadly to the act of creation itself rather than to the finished characters or narrative. "Realistic" describes a style or approach in literature that seeks to portray life accurately, often using real events rather than those that are invented. Hence, "fictional" is the most appropriate choice for describing creations stemming from an author's imagination.