A cross-reference is a note in a book, article, or document that tells you where to find related information in another part of the same work. When you're reading an encyclopedia entry about owls and see “see also: raptors, page 156,” that's a cross-reference pointing you toward more useful information.

Cross-references work like a helpful guide saying “if you're interested in this, you should also look over there.” In a textbook, you might see “for more on photosynthesis, see Chapter 4.” In a dictionary, definitions often include cross-references to related words: affect might tell you to compare it with effect.

The word can also be a verb. When you cross-reference two sources, you're checking them against each other to verify facts or find connections. A detective might cross-reference witness statements to see if the stories match up. A student researching ancient Egypt might cross-reference different history books to make sure the dates are accurate.

Before computers, cross-references required flipping through pages. Now digital documents use hyperlinks as instant cross-references. But the purpose remains the same: helping you discover related information and build a fuller understanding of your subject. Good cross-references turn individual facts into connected knowledge.