Cross-AZ traffic
The 8% network line is the cross-zone chatter cost. It is not a GCP-only surprise: AWS bills the same cross-AZ traffic at $0.01 per GB each direction, so this workload would cost about the same on AWS. The mitigation is the same on both clouds: pin the workloads to a single zone (accept reduced AZ-failure tolerance) or use regional persistent disks instead of cross-zone replication.
Read the term in context.
Each row is a lesson that uses this term. The lesson where it first appears is the canonical definition.