What is a reusable Service?

It’s a self-contained, reusable, discoverable, stateless capability with the required granularity that may be used in a composite application or service. A reusable service should be associated with a business activity that the service requirements define (design-time contract).

Different run-time contracts, numerous interfaces (the WSDL for a SOAP Web Service), and multiple implementations can specify a service’s restrictions, such as security, QoS, SLA, and use policies (the code).
Throughout its entire lifespan, from design to runtime, a reusable service should be regulated at the corporate level. Its reuse should be encouraged through a prescribed method, and the amount of time it is used should be tracked.

A resource that is not rendered useless by being used; for example, a central processing unit (CPU) of a computer or the tape transport, i.e. a magnetic tape player or recorder, including the head, capstan, pinch roller, tape pins, and tape guide. Magnetic disks or tapes can often be used indefinitely and are to be regarded as reusable resources.

Renewable or reusable resource is a resource which can reused repeatedly and does not run out because it is naturally replaced. For eg solar energy, wind energy and geothermal process.