What is a meta description?
A meta description is an HTML tag that provides a brief summary that outlines the content on your webpage. The description should be no longer than 155 characters. Search engines show the meta description in the search results mostly when the searched phrase is within the description.
Here is what the description looks like in the HTML code:
<meta name="description" content="This is an example of a meta description. This will often show up in search results.">
Here is what the meta description looks like in the SERP (Search Engine Results Page):

Are Meta Descriptions an SEO ranking factor?
No, the meta description is not an SEO ranking factor. Back in September 2009 Google announced that neither meta descriptions nor meta keywords would factor into their ranking algorithms.
Some advice – Make sure you add in your keyword and keyword avariations into yoru meta description. You may notice when you search for a given search term, in this instance lets say my search term is ‘iPhone 13 Pro’, you see that the specific search term I searched for is shown in BOLD text in the meta descriptions. Whilst its not a rankign factor, having your keyword in your meta descrtion may help with your CTR. See example below.

Why do meta description differ in the SERP results from the one you created?
Google wants to present the most relevant detail to meet the search request. In some instances you may find that the meta description you have set up within your page does not match the SERP result. Do not worry about this though, Google will select text from your page that is relevant to the search request and present it in your meta description which in turn may increase your CTR (Click through rate). This makes it even more important to ensure that your content is clearly laid out and easy to navigate not just for Google but for your potential site visitors.
Make sure your your meta description matches the content on the page.
This point is very important. Google will know if you try to trick visitors to click through on your page using a meta description is no relevant to your content, this could casue you headaches further down the line with Google potentially even penalizing you so don’t risk it. Also, entering a misleading description will increase your bounce rate and in turn will lower visitors trust in your blog, business or shop so avoid it at all costs and be true to your content.
You can learn more about meta tags here: A quick and easy guide to meta tags in SEO 2023