A job description is an internal document that clearly states the essential job requirements, job duties, responsibilities, and skills required to perform a specific role. A more detailed job description will cover how success is measured in the role so it can be used during performance evaluations. They are also known as a job specification, JD, and position description (job PD).
Here’s a sample of job descriptions, ranked from good to bad. Looking through them alongside their scores makes it obvious why some are better than others, and is a good exercise to teach yourself to get better at writing them.