Biological Chronicle is what it means.
Common misconception. The original idea for Bionicle was conceived by Christian Faber when imagining the pills he was taking for an illness at the time were actually transports for tiny soldiers that would fight his disease inside him.
It's from that we get the Toa, Toa canisters, the Mata-Nui Robot, and the Makuta Virus. It's a chronicle of biology. A BIOlogical chroNICLE.