The NIST (National Institute of Standards and Technology) defines the essential characteristics of cloud computing as:

On-demand self-service: Users can provision and manage computing resources automatically without requiring human intervention from the service provider.

Broad network access: Cloud services are accessible over the network through standard mechanisms, enabling access from various devices and locations.

Resource pooling: Cloud providers pool computing resources to serve multiple consumers, with resources dynamically assigned and reassigned according to demand.

Rapid elasticity: Cloud resources can be rapidly scaled up or down to meet varying demand.

Measured service: Cloud services are metered, and customers pay based on their usage, which allows for cost efficiency.

These characteristics define how cloud computing services are provided and accessed, focusing on flexibility, scalability, and efficiency.