The command-line tool for managing Google Cloud resources. It includes gcloud and other tools such as bq and kubectl, and lets you save named configurations (account, project, region, and zone). It comes preinstalled in Cloud Shell.
The ACE has many command questions: gcloud services enable, gcloud projects add-iam-policy-binding, gcloud compute instances create, gcloud container clusters get-credentials, or gcloud storage cp.
Google Cloud CLI (gcloud) is a concept that can show up on the exam. Check the full guide to see it in context.