Ibid. is an abbreviation for the Latin word ibidem meaning “in the same place.” The phrase is useful for citations and bibliographies to refer to a source cited in a previous entry, possibly appearing in a citations page as:
 Cicero, M.T. Latin 101 (Rome: Academic, 21 BCE), p. 4.
Ibid. is always followed by a period, is capitalized only at the beginning of a sentence or citation, and may or may not be italicized depending on the writer’s preference.