Cross-Linking.

Cross-linking is the practice of linking between two or more separate websites that share the same owner or are operated by entities with a relationship. In legitimate use, it describes simple interlinking between genuinely separate but related sites (a company linking to its sister brands). In its problematic form, it refers to creating networks of sites that link to each other primarily to artificially inflate PageRank, a link manipulation scheme Google actively penalises.

Cross-Linking vs Internal Linking vs External Linking

Internal linking connects pages within the same domain. External linking points to a different, unrelated domain. Cross-linking sits between these: linking between domains that share ownership or are operated by the same organisation. Google's Webmaster Guidelines flag 'excessive link exchanges' and linking between sites 'for the sole purpose of cross-linking' as link scheme violations, particularly when anchor text is keyword-optimised.

When Cross-Linking is Legitimate

Cross-linking between genuinely separate businesses with a natural relationship is not inherently problematic. A law firm's website linking to its founder's personal blog; a brand linking to a subsidiary's product site; a media group linking between its publications, all of these have editorial justification. The test is whether the link is useful to the reader and editorially warranted. Cross-linking that exists solely to manipulate PageRank, such as a network of microsites all pointing to a money site, violates Google's guidelines.