The Discovery plugin is about discovering, or finding, implementations for pluggable interfaces. Pluggable interfaces are specified with the intent that at least one implementation will be available to provide the service described by the interface.
In the absence of a common service for discoverying interface implementations many components invent design and implementation principles for self-discovery. A standard Discovery facility is required to provide a consistent and obvious way to discover service providers.
The JLense Discovery plugin is a wrapper around the Jakarta Commons Discovery tool. The JLense Discovery plugin also defines extension points that other plugins may use to register service providers with the Discovery facility via standard plugin extension definitions. See the description of the org.apache.commons.discovery.services extension point.