Abstraction. often via virtualization. frees the resources from their physical constraints to enable pooling. Then a set of core connectivity and delivery tools(orchestration)ties these abstracted resources together. creates the pools. and provides the automation to deliver them to customers.
Ref: CSA Security Guidelines V4.0

In IaaS service model. CSP is responsible only for the physical infrastructure.

The management plane controls and configures the metastructure, and is also part of the metastructure itself. As a reminder, cloud computing is the act of taking physical assets (like networks and processors) and using them to build resource pools. Meta structure is the glue and guts to create, provision, and deprovision the pools. The management plane includes the interfaces for building and managing the cloud itself, but also the interfaces for cloud users to manage their own allocated resources of the cloud.
Ref: CSA Security Guidelines v4.0