What does Idem mean? from mypaperwrite's blog

For your professional research paper, you have to know how to quote. Write idem (abbreviation is.) If an author's work is quoted at the foot of the page and the other works of the same author are quoted, not interspersed with the works of other authors, the idem followed by the title of the work and the other data is put instead of his name. The quoted work, abbreviated op.cit. (In Latin, opera citato -  cited paper) is an indication following the name of an author followed by the link to the page where the quote is found.

This abbreviation op.cit. thus indicates the volume that was previously specified on another page and implies that there is no other work of the same author between the base reference and the repeated reference. In the place quoted (loc.cit from latin loco citato) is the heading that follows the title. This abbreviation is used when the base reference is separated from the referenced reference by other references in order not to repeat the place. Both op cit  and loc.cit. refer to previously cited works on other pages where all bibliographic data has been mentioned.