What characteristic is central to the definition of Infrastructure as a Service (IaaS)?

Infrastructure as a Service (IaaS) is primarily defined by its focus on delivering virtualized computing resources over the internet. This model involves the provision of essential hardware components such as servers, storage, and networking infrastructure, which users can leverage to build and manage their own applications and services.

The characteristic of provisioning hardware resources only emphasizes that IaaS allows users to rent or purchase essential infrastructure rather than having to invest in physical hardware, which can be costly and require significant maintenance. This model provides scalability, allowing users to adjust their resources based on demand, and fosters flexibility in deploying applications without the overhead costs associated with on-premises hardware management.

The other options focus on different aspects of cloud services that are not central to the definition of IaaS. For example, delivering applications via the internet aligns more with Software as a Service (SaaS), while complete application customization would pertain to more tailored service models. Managing full IT service delivery introduces elements of IT management that extend beyond the core premise of resource provisioning fundamental to IaaS.