A job description is a summary of important details of a specific vacancy or position within a business. It explains the remit of the role (eg types of work involved and responsibilities), any requirements for applicants (eg skills, experience and qualifications) and the benefits (eg salary and other staff perks).
Writing a job specification helps ensure that only the most suitable and qualified candidates apply for a position. This reduces time spent on filtering applications by management and HR. It also helps existing employees who are moving to a different role within a business understand their new roles and responsibilities.