What is a basic difference between job specifications and job descriptions?

A job description will outline the tasks and responsibilities of an employee for a given position - the day-to-day work that the prospective candidate can expect to fulfill if they get the job. A job specifications section of an job advertisement will detail what sorts of qualifications the employer expects a candidate to possess to fulfill the responsibilities given in the job description. Employers expect that certain educational or work related experiences will allow prospective candidates to thrive in the position, and these specifications differ between positions.