Abbreviation for ibidem, meaning "in the same place; in the same book; on the same page."

Generally used for references and the source for ibid will be found in the reference just before it. When you are giving reference to a book

3. Guide to Excise Valuation page 213

4. ibid page 397

This would mean that the reference in 4 is the same as in 3, namely Guide to Excise Valuation, but as can be seen the page number is different.