A meta description is a short HTML snippet, usually around 150 characters, that summarises what a page is about. Search engines often display it beneath the page title in results. It carries no direct ranking weight, but a sharp one lifts click-through rate.
The text lives in the head of your HTML as one of the page's meta tags and never appears on the visible page. Its main stage is the search snippet. Google frequently rewrites it, pulling a sentence from your body copy when that better matches the query, so treat your written description as a strong suggestion rather than a guarantee. When Google does keep it, a benefit-led line earns more clicks than a vague one.
A Toronto bakery ran this description on its wedding-cake page: "We make cakes for all occasions in the GTA." Flat, and it competed with a dozen near-identical lines. Rewritten to "Hand-piped wedding cakes in Toronto — tastings 7 days a week, order 3 weeks ahead," the snippet spoke to intent: location, a reason to act, and the lead-time answer people actually search for. Over the next month the page's click-through rate rose from about 2.1% to 3.4% at a steady average position.
A well-written description works together with the page title and is a small but real part of good on-page SEO.