In one sentence
A Citation is when a generative AI references a web page, company, or piece of data as its "source" (i.e., as evidence) while producing an answer. It is one of the most important metrics in GEO.
What does it look like in practice?
For example, when you ask Perplexity "What's the market size of B2B SaaS?", you might get something like:
The domestic B2B SaaS market is forecast to keep expanding (Sources: ○○ Research Report, △△ Industry Journal).
Here, research firms and industry media are cited as the basis for the answer.