The meta description is not visible in any part of your site, except if you check the actual HTML code. It is meant as a means to configure a short summary of the content of the page you currently are.
If set up correctly it is actually used by search engines like Google, Bing and Yahoo as the snippet found in the Search Engine result Pages (SERP's) to describe a search result for a webpage. Therefore, you can also see it as the sales pitch to your website, as it can trigger people to actually click on your result in Google:
Actually, the meta description is NOT used as a factor weighing in the search rankings, which sometimes causes people to think it is not important from an SEO perspective. However, their impact on Click Through Rates can be massive. The best way to describe it's importance is that you can see it as a little advertisement for your website, for free... Similar to the page title, attractive meta descriptions are very important.
The only thing Google hates is duplicate meta descriptions. They even stated on their webmaster blog that you are better off having empty meta descriptions then duplicate ones. If you do not enter the meta description for your pages, Google will just try and take a snippet from the text of your page. Usually, it will do a pretty good job in doing so, except that it will usually look a bit messy, with sentences broken off, and the use of '....'.
However, if you enter the meta-description yourself, you have full control of this text, as long as it is relevant for your search results. If a user searches for the word "SEO", but the meta description you filled in does not contain this word, Google will probably ignore your description and use it's own. Using a correct meta-description has the following advantages:
- If you make sure you limit the description to 160 characters, it will not be broken off, and won't look messy.
- If carefully composed, users browsing through the search results may be more likely to click you site, increasing the Click Through Rate (CTR), which in itself can be positive for your SEO ranking.
- Google does NOT use meta descriptions to rank you higher. However, if set-up correctly, Google might register the higher CTR and reward you for this.
- Google hates duplicate meta descriptions. That could mean that it is better to have no meta description at all then one meta description for all pages on your site. This is a topic of much debate in the SEO world....
Setting a global meta-description in Joomla
When building a Joomla site, the first thing you are often advised to do is to add a global meta-description, using the Global Configuration settings. This ensures that every page will have a meta-description. However, it will be the same for all pages of your site, which is why I personally leave it empty (I add it for individual pages later). If you want to use it though, you can enable it from:
System > Global Configuration > Site tab, under Meta-Data
In the Site Meta Description field, fill in a useful description, using your main keywords:
Meta-description for every page
You should make sure that every page will have its unique description, at least the ones you want indexed. Then every page can build its own ranking for its own specific keyword or keyword-combintion. In some cases, you might even manage to get several pages of your site listed on a Google search page.
You can set your descriptions on either article, category or menu-level. If you have a simple site with only a few articles, where every article is linked to a menu-item, it does not really matter which one you choose. On larger sites, or sites using blog-views, not every page is connected to a menu-item. Probably the best way to go is to set it in every article, for category views per category, and for the remaining ones on menu-level.
The most used method is the Article Manager:
You can also choose to set meta description from the menu-items. If both are entered, the menu-item description will be used.
Again, there are a lot of Joomla extensions that can help you with this process. In the JED you will find extensions that can even automate the process of generating meta-data for you: http://extensions.joomla.org/extensions/site-management/seo-a-metadata/meta-data. These extensions could work fine, but you have less control over the exact descriptions used. Often, they just pick the first 160 characters of an article. An example of a popular one that works quite well is Easy Frontend SEO.
Other extensions provide a clean overview for updating this information instead of having to go into each separate article every time. Most of the better SEF extensions like SH404SEF, MijoSEF, JoomAce etc. have this feature built in, but there are also extensions that provide just this functionality. One extension that I can highly recommend is OSmeta. It is easy to use and gives you a perfect overview.
Pro-tip: It is always wise to perform an SEO audit that also scans whether your meta descriptions are indeed set-up correctly. I can highly recommend Onpage.org for this. It's free for one website (read my review of this service).