Novella is a genre of prose fiction that is longer than a short story but shorter than a novel. While there's no strict word count, it generally falls between 17,500 and 40,000 words.
Other literary terms that might fit your criteria include:
* Long short story: Some consider stories above 7,500 words to be long short stories.
* Mid-length novel: This is a somewhat informal term, but some novels might be considered "mid-length" if they fall between 20,000 and 50,000 words.
Ultimately, the word count is just a guideline, and the most important factor is the story itself. A narrative can be captivating regardless of its length.