"Call" in the call money market originally meant money that comes back as soon as it is called (money at call)1. It is a different thing from the "call" that is short for a call option. The call money market is a place to lend and borrow short-term funds, while a call option is a right to buy the underlying asset. This site tells them apart by context.

Participants are financial institutions such as banks, insurance companies and securities companies, together with the money brokers (tanshi companies) that intermediate trades1. There are secured call transactions, with collateral, and unsecured call transactions, without it. In unsecured call, the overnight transaction, in which funds are handed over on the trade date and returned on the next business day, is the main form1.

TONA is the benchmark rate that the Bank of Japan publishes each business day, based on overnight unsecured call transactions2.

Notes

  1. Bank of Japan, "コール市場" (Call money market) (Oshiete! Nichigin, in Japanese). Paragraph 1 (money at call), paragraph 2 (participants), paragraph 3 (secured and unsecured), paragraph 5 (overnight is the main form). ↩ ↩2 ↩3

  2. Bank of Japan, "リスク・フリー・レートに関する勉強会" (Study Group on Risk-Free Reference Rates), OIS materials (in Japanese; the Bank of Japan publishes the final unsecured overnight call rate). ↩