Which one of the following options can be considered as the Cloud?

Concept

In cloud computing, "the Cloud" refers to a pool of physical computing resources (storage, memory, processing power) that has been abstracted behind a single logical interface, so a user or application interacts with the pool as one unified resource without needing to track or manage the individual physical machines behind it.

Application

Hadoop is exactly this kind of abstraction: it is a framework that clusters many ordinary physical machines and presents them to the user as a single distributed storage-and-processing resource (HDFS for storage, MapReduce/YARN for processing) -- a user stores a file or submits a job without needing to know which physical node holds which block. That physical-to-logical abstraction is the defining trait of cloud computing, which is why Hadoop is identified as "the Cloud" among the options given here.

Contrast

Contrast with the other options:

• Intranet: a private organizational network with a fixed, known set of machines. It approaches cloud-like behaviour only once it grows too large to track individually -- as an ordinary intranet it does not itself embody the abstraction.

• Web Applications: software a user accesses over the internet. A web application typically runs on cloud infrastructure -- it is a hosted service, not the underlying physical-to-logical abstraction that "the Cloud" refers to.

• All of the mentioned: this only holds if every option equally satisfies the definition. Since a private network and a hosted application are, at best, adjacent to or built on the cloud rather than being the abstraction itself, singling out Hadoop is the more precise reading among the choices offered.

Note: this is a widely circulated interview-style quiz item, and differently-ordered copies of it circulate online; the analysis above reflects the standard reading this item is keyed against.