Here's why:
* Brief piece of prose: Essays are typically shorter than novels or other long-form works.
* Single subject: Essays focus on a specific topic, allowing for in-depth exploration.
* Highly opinionated: Personal essays and opinion pieces often express the writer's personal thoughts and perspectives on the subject.
Other possibilities:
While essay is the most common fit, other options could include:
* Editorial: This is a piece specifically designed to express the opinion of a publication.
* Blog post: Many blogs feature short, opinionated pieces on various subjects.
* Review: A review often offers a personal opinion on a product, book, film, or other subject.
Ultimately, the specific genre depends on the context and the writer's purpose.