A complementary currency is a currency which complements the state's currency system. The intention involved in the creation of a (complementary) currency determines its construction.
The state's currency serves the processing of business transactions in a competition-oriented "free market" (yang) economy. It is scarce by design, since the interest needed to fully repay a loan is never created, the banks can always only lend the principal sum. Thus money capital is in the foreground of the competition-orientated economy.
A complementary currency is used for market transactions in a cooperative (yin) economy which puts the social capital in the foreground. It is intended to support society and there should always be enough available. In order to keep the means of exchange readily available, many complementary currencies are defined as mutual credit systems and equipped with a circulation safeguard (demurrage).
The complementary currency suggested in this concept, the Grok, uses a demurrage – but is not a classical mutual credit system. It is a user-emitted and secured currency, which comes into existence only when linked to deposited securities (e.g. previous investments in the CPO).