Meta Description
A meta description is an HTML element in a page’s head that offers a short summary of the page for search engines to show beneath the title in results. It is a suggestion: Google states that snippets are created primarily from page content and that the meta description is used when it gives a more accurate account.
What Google does with it
According to Google’s documentation on snippets, the text under a result is generated automatically from the page, chosen to emphasise what is relevant to the particular search, and the meta description is substituted when it describes the page better than the extracted content would. There is no stated length limit; the snippet is truncated to fit the device. The document does not describe the element as a ranking signal. So the meta description is a bid for the two lines a searcher reads before clicking, accepted or declined query by query.
The description and the assistant
An assistant that fetches the page reads the body. A summary written for the results page, however good, is not the passage it lifts, and a description that promises what the body does not deliver helps nobody. The useful discipline is to write the description as the page’s answer in one sentence and then make sure a sentence in the body says the same thing, so the two readers, the searcher skimming results and the assistant looking for a span, get one account of the page. On this site each glossary term’s definition is the first sentence of its page and of its structured data for that reason.
A common question
Does the meta description affect what an AI assistant quotes from a page?
No, because an assistant that fetches the page reads the body. A summary written for the results listing is not the span it lifts, and a description promising something the body never states helps neither reader. The useful discipline runs the other way: write the description as the page's answer in one sentence, then make sure a sentence in the body says the same thing, so the searcher skimming results and the assistant hunting for a passage get one account of the page.
Related terms
Sources
Snippet behavior: Google Search Central, snippets. This entry carries no figures.