a reference that tightly binds one reference to another, so that for using the referencing reference it is also necessary to have the cross-referenced reference

A project which facilitates linking from cited references to full text on publisher websites. CrossRef uses the DOI to transmit citation information from which links are generated. (Source: "E-journals: access and management" Library Technology Reports http://www.techsource.ala.org)

A crossref is a reference which tightly binds one reference to another, so that for using the referencing reference it is also necessary to have the crossreferenced reference. Crossrefs are mirroring BibTeX's concept of a crossref field and are used to avoid redundancies when dealing with references to a resource which contains a number of sub-resources which should also be referenced (such as a book containing chapters which should be referenced as individual resources). A crossref is different from an xref, because the crossref represents an inherent (i.e., on the resource level) relation between the resources, whereas an xref represents a conceptual association between otherwise independent resources.