Ibid is the way of referencing an already cited work before on that page of text.
It's a Latin term that means in the same place, and is used as a bibliographic reference in Brazil, along with other Latin expressions such as idem and apud.
According to the Brazilian Association of Technical Standards, ABNT, the term ibidem replaces the citation of work and page cited above on the same page of the scientific text.
According to ABNT rules, the first citation of an author and work must present the full reference. Later references are replaced by Latin expressions to avoid repetition.
Ibidem is used in footnotes to replace the name of the work, when it has already been mentioned and only changes the reference page.
Example:
1 BAUMAN, 2001. p.36.
2 Ibid., p.49. (or Ibid., p. 49)
Ibid is the abbreviation for Ibidem.
Idem and Ibid.
Idem is also a Latin word used in bibliographical references. Idem means "the same", and is used to quote the same previously mentioned author and thus avoid repetition.
While Ibidem means in the same place, that is, in the same book or the same page.
So the use of idem and ibidem simultaneously in the references is redundant, as ibidem already presupposes that it is the same author, since it is the same work.
See also the meaning of Idem.