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.
Write a description of your company or organization. This overview will be included with all job descriptions, to give a sense of your workplace. Thus, it can be written ahead of time so that it can be inserted into the template when you prepare it.