The job description focuses on the essence of the job itself.
Job specifications focus on the qualifications needed to perform the job and are technically included within a job description.
The terms job posting, job description and job specification are frequently (and incorrectly) used interchangeably. A job posting may contain elements of the job and the qualifications needed but it is usually a shortened version designed for recruiting purposes.
It’s generally safest to have standardized, documented, and compliant job descriptions to ensure that employees clearly understand job expectations.