How do search engines use meta descriptions?

The meta description or sometimes just description is the name="description" content=""/> HTML tag in the of a webpage.

Visitors to your website can't see it at all on the page. Search engines use it as the paragraph text in search results:

(it's the 'Visit Dunnottar Castle for an...' text). They don't look the keywords in here for ranking.

Meta descriptions also appear sometimes when sharing on social media.

For SEO, the main purpose of a meta description is to encourage a user to press your search result rather than someone else's. You'll notice too that sometimes keywords are made bold depending on what the user has searched for.

Unique

Every meta description on your site should be unique. If a unique meta description can't be generated it is best practice to leave it off of the page entirely. Search engines can do a pretty good job of generating some text from the page contents themselves. Depending on what the user has searched for a search engine may also decide not to show your meta description and display some other text that matches better.

Describes the page

A meta description shouldn't be the same text throughout your entire site. It should describe the specific page.

Compelling copy

You are writing primarily to encourage a user to visit your page here- your target isn't to include as many keywords as possible. Write in a human way using sentences rather than lists of keywords.

Why would a searcher visit your page/site rather than somewhere else? That's what to bear in mind when writing your meta description copy.

Containing good keywords

Even though the keywords you use here won't be considered by search engines for ranking, as mentioned they are often made bold if they match the user's search- drawing their eye. If they're looking for a specific thing including that phrase in your copy will make your result more attractive rather than abstract generalities.

Length

Search engines will truncate (cut off) any text over around 160 characters. Make sure you express a coherent and compelling description in under 160 characters. Sometimes a little less or a little more is shown, but 160 is by far the majority of search results.

Only one

There should be just one meta description in the head of your page. More than one and a search engine will arbitrarily select one or ignore it.

It isn't showing up in search results

As mentioned above, search engines won't always use the meta description for the paragraph text. But if they're showing an old meta description or the page doesn't appear in search results give these a shot:

• Make a tangible change to the page to prompt it to be re-indexed. For a product page this could be making the product description longer or changing images. Search engines often won't re-index a page if the meta description is the only thing that has changed on it.
• Wait at least a couple of weeks. Search engines don't instantly pick up changes to your shop.
• Check for any issues in Plug in SEO, Google Search Console and Bing Webmaster Tools and fix them

Unfortunately sometimes search engines stubbornly just won't re-index a page! That gets more rare if you have made substantial changes to the page.