For example google's page shows a description:
In their case the text is
Search the world's information, including webpages, images, video's and more. Google has many special features to help you find exactly what you're looking ...
I've looked at the source of their page to find how this text is determined but could find nothing. Google also has a nice page explaining how to make descriptions, but never specify where to put the description.
Someone told me the description should be in the robots.txt, but when looking at the specification of robots.txt it only has four keywords:
- user-agent (start of group)
- disallow (only valid as a group-member record)
- allow (only valid as a group-member record)
- sitemap (non-group record)
None of them are description or search tags.
The snippet is often taken from the description meta tag:
which is placed between the page's
<head> </head>tags.What actually shows to the user is completely at the discretion of Google's algorithms - it may decide that another section of text on that page is more relevant to the user's search.