What is the meaning of Koji?

A substance that is produced by letting a mold, especially Aspergillus oryzae, grow on rice, barley, soybeans, etc., used to make fermented products such as sake, amazake, miso, and soy sauce.

The mold used in such a preparation.

Rōmaji transcription of こじ

which, what

which, that, who, whom

some, few

what a/an, what the (used to express astonishment, anger or incredulity)

Source: wiktionary.org