Virtual organization refers to a set of individuals or institutions that share the same resources, follow a well-defined policy, use and develop the same software, etc. They are temporary or permanent entities, based on a common research field or a project.
SLING clusters all support gen.vo.sling.si VO.
Users can be members of multiple VOs. And each cluster can support multiple different VOs.
The list of registered VO-s in the EGI infrastructure is available on https://operations-portal.egi.eu/saml/discovery