The term cross-reference (abbreviation: xref) 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-referencing is maintained to a document with either in-context (XRIC) or out-of-context (XROC) cross-referencing. These are similar to KWIC and KWOC.
• 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.