The term cross-reference can refer to either:

• An instance within a document which refers to related information elsewhere in the same document. In both printed and online dictionaries cross-references are important because they form a network structure of relations existing between different parts of data, dictionary-internal as well as dictionary external.
• In an index, a cross-reference is often denoted by See also. For example, under the term Albert Einstein in the index of a book about Nobel Laureates, there may be the cross-reference See also: Einstein, Albert.
• In hypertext, cross-references take the form of "live" references within the text that, when activated by mouse click, touch, voice command or other means, immediately makes available the referenced content, which might be a different part of the same document, or another document entirely.
• In programming, "cross-referencing" means the listing of every file name and line number where a given named identifier occurs within the program's source tree.
• In a relational database management system, a table can have an xref as prefix or suffix to indicate it is a cross-reference table that joins two or more tables together via primary key.