Every page on your website can have a short textual description associated with it. This description is sometimes used by search engines or other websites to summaries what your websites page is about (Google calls it the "snippet"). Here's an example where Google has included part of my home pages description in my entry in its search results:
The description text is quite prominent in the search results list. It should be used as a great SEO marketing tool by encouraging people to visit your website. A description that stands out or even has a call to action has a greater chance in getting clicked on, thus generating more visitors to your website.
Your Page Titles are also a very important element to SEO.
A simple way to test your descriptions is to search Google so that your website shows up in the results. If Google has indexed your website then a search in the following form will show most of your pages and how their descriptions are displayed:
I've also developed a Google Search Result Emulator Tool that lets you test different descriptions to see how they may look in Google's Search Results.
The description text can be defined on every page in your website.
If you use a Content Management System (CMS) to edit your website it will most probably provide a field to enter each pages description.
If not, then you will have to edit the html for each page. The description text is placed in a <meta> tag that should be in the head section. Here is the part where a description is defined:
<html> <head> <title>How to add a Meta Description - Web Site Advantage - Adelaide</title> <meta name="description" content="The Meta Description provides a summary of your pages for use by other websites, such as Google in their search results. Find out More." /> ... </head> ...
Google and other search engines show upto 4 lines of summary for each page in their results, that's from about 160 to 320 characters. Make sure your message is concise and inside that allowance. Over large descriptions may make search engines think you are spamming them!
Every page on your website is a potential advert for you. A common mistake is to use the same description throughout the website. This is a major waste as you could have every page target different market sectors instead of targeting a single one. So every page should have a unique description, and that description should relate to and promote the contents of the page.
The description should be designed to make a searcher think "That's the website I need". Make it compelling. Tell them how it will answer their question, solve their problem or make their life better.
Google highlights a users search words in the result summary, so it is best to try and include the common keywords related to the page. The highlighted words will attract attention.
The description comes under the title. So don't duplicate information. Make the title and description work together to sell your page.
Google, via their Google Search Console (Google Webmaster Tools) will tell you what they think of your descriptions. They will indicate where you have duplicate descriptions or descriptions that are not of a good length.