The meta description is a <meta name="description"> tag in your HTML <head> that provides a summary of the page. Search engines often (but not always) display it as the snippet below your title in results. It doesn't directly influence rankings — Google confirmed this years ago — but it massively influences whether people click your result.
Think of it as ad copy for organic search. You're competing with 9 other results on the page. A compelling meta description with a clear benefit and implicit call to action gets more clicks than a generic one — and higher CTR does indirectly improve rankings over time because Google sees your result satisfying searcher intent.
Writing descriptions that actually get clicked
Keep it under 155 characters (Google truncates around 155-160). Lead with the benefit, not the feature. Include your primary keyword naturally — Google bolds matching terms in the snippet, which draws the eye. End with something that creates forward momentum: a number, a promise, or an implied action. "Here's how" or "See the data" outperform generic endings.
The biggest mistake: leaving the meta description blank and hoping Google generates a good one. Sometimes Google does pull a decent excerpt from your page. Often it pulls something random and unhelpful. For landing pages where you're paying for traffic or competing for organic clicks, write every meta description deliberately. It takes 60 seconds and affects every impression your page gets.