Auxiliary Proof-of-Work (POW)
a.k.a "AuxPOW". This is the way that merged mining can exist; it is the relationship between two blockchains for one to trust the other's work as their own and accept AuxPOW blocks.
Advantages of AuxPow
Merge Mining, or AuxPow, allows the work being done for a parent coin (such as Bitcoin or Litecoin) to be used to find valid blocks on Terracoin's blockchain.
Mining with AuxPow
Information on mining AuxPow can be found in the Mining Section