The phrase "separate sheet" refers to a piece of paper or document that is not connected or attached to something else. It is used when you need to provide additional information or write something separately from the main document. Full definition
The large scale drawing (three metres by two metres wide) is made up of separate sheets of papers that combine to form a singular large work. (contemporaryartsociety.org)
It is recommended to avoid writing references and their contact details within the resume and be given on separate sheet of paper only when asked. (bestsampleresume.com)
Gone are the days when candidates submitted separate sheets of references that the recruiter could call up to hear some praise. (velvetjobs.com)