Explanation/Reference:
The term utility computing is often used to describe the metered (or pay-per-use) IT services enabled by grid computing. Cloud computing (where dynamically scalable and often virtualized resources are provided as a service over the internet) is another term that describes how enterprises are using computing resources-on both private and public networks-over the internet.
Because grid computing provides superior flexibility, it is the natural architectural foundation for both utility and cloud computing.
Reference: Oracle White Paper, Oracle Grid Computing