A counterbrockage error involves a capped die and a previously struck coin. When a capped die strikes a previously struck coin, the obverse design from that struck coin will be impressed into the cap. The result will be a design where the cap face will be an incuse brockage. When a new blank is struck by this capped die with an incuse brockage image, the obverse will have a raised and spread image from that incuse design of the cap. This brockage impression is known as a counterbrockage.

Images courtesy of Byers Numismatic Corp.

Significant examples:
Famous Liberty Nickel Counterbrockage  (illustrated above).  Pictured in Taxay and Margolis/Weinberg.

Sources and/or recommended reading: