Multitenancy is a fundamental architectural principle in cloud computing where a single instance of software and its supporting infrastructure serves multiple customers, known as "tenants." Each tenant shares the application and computational resources (e.g., processing, memory, storage) but their data, configurations, and user management are logically isolated and secured from one another. This model allows cloud providers to achieve significant economies of scale and operational efficiency by pooling resources, which is a core tenet of public cloud services (SaaS, PaaS, IaaS).

A. This describes resource isolation, which is a necessary component of a multitenant architecture to ensure security, but not its defining characteristic, which is resource sharing.

C. This describes a geographically distributed or multi-region architecture, which is a strategy for resilience and latency reduction, not multitenancy.

D. This describes network slicing, a concept primarily used in 5G to create virtualized, end-to-end networks on a common physical infrastructure, which is a specific use case and not the general definition of multitenancy.

1. Mell, P., & Grance, T. (2011). The NIST Definition of Cloud Computing (Special Publication 800-145). National Institute of Standards and Technology. In Section 2, "Essential Characteristics," the concept of "Resource Pooling" explicitly states: "The provider’s computing resources are pooled to serve multiple consumers using a multi-tenant model..." This directly supports that multitenancy involves shared resources for several customers.

2. Nokia. (2020). Cloud-native design for 5G core: The foundation for a successful 5G business [White Paper]. The paper discusses cloud-native principles, where multitenancy is a key enabler for efficiently running network functions for different customers (tenants) on a shared cloud infrastructure, aligning with the definition of shared resources.

3. Chappell, D. (2011). The Essential Guide to Cloud-Native for Telcos. David Chappell & Associates. Chapter 2, "Understanding Cloud Platforms," defines multitenancy as a primary characteristic of public cloud platforms, allowing multiple customers to share the same infrastructure while maintaining isolation. This is a foundational text often referenced in telco cloud courseware.