Shared resources refer to when the infrastructure and computing resources are used by multiple clients, or 'tenants,' in a cloud environment. This allows for cost savings and increased efficiency as it leverages economies of scale. 'Rapid elasticity' is incorrect because it refers to the quick scaling of resources to meet demand, not sharing of components. 'Metered utilization' accurately describes how cloud service usage is measured and paid for, but doesn't capture the concept of resource sharing among multiple clients. 'File synchronization' involves ensuring files are updated across systems and devices and does not inherently involve sharing fundamental infrastructure components.