From Science Europe Data Glossary
Definition: metadata harvesting is an automated, regular process of collecting metadata descriptions from different sources to create useful aggregations, so that services can be built using metadata from many repositories.
Explanation: the Open Archives Initiative Protocol for Metadata Harvesting (OAI-PMH) is widely used for metadata harvesting. An implementation of OAI-PMH must support representing metadata according to the Dublin Core standard, but may also support additional representations. The Dublin Core Schema is a small set of vocabulary terms that can be used to describe web resources (video, images, web pages, etc.), as well as physical resources such as books or CDs, and objects like artworks.