A job specification could be considered a more precise job description that details the exact educational degrees, experience, skills, and requirements for a role. In most cases, these terms are used interchangeably and nearly always describe the same document.
A job description or JD is a document that describes the general tasks, or other related duties, and responsibilities of a position. It may specify the functionary to whom the position reports, specifications such as the qualifications or skills needed by the person in the job, and a salary range. Job descriptions are usually narrative, but some may comprise a simple list of competencies; for instance, strategic human resource planning methodologies may be used to develop a competency architecture for an organization, from which job descriptions are built as a shortlist of competencies