Ibid vs idem
Ibid is an abbreviation of ibidem, a Latin word that means, literally, in the same place. Ibid is used mainly in footnotes or references to note a source that was previously mentioned, saving time and space by not repeating the same thing over and over again. Note here that it is the exact same source in the exact same place, so the duplicate citation would be exactly the same. Some style guides and dictionaries will tell you to use a period with ibid., others will …