Plus One (or +1) is Google's answer to the Facebook Likes button. This appears as a white and blue button next to the Google search results on on a particular web page.  The button allows Google to perform a mini-user poll and thereby (supposedly) enhance the search experience based on this feedback. This also integrates social interaction into determining the quality of the content.

The Plus One button appears in the Google seach list and can be included on a page or article if the code is included in any website.

Google still are experimenting with Plus One and the way that it is used for search (and real time search) will change over time.

+1 helps people discover relevant content—a website, a Google search result, or an ad—from the people they already know and trust. Adding the +1 button to your pages lets users recommend your content, knowing that their friends and contacts will see their recommendation when it’s most relevant—in the context of Google search results.

When a signed-in Google user is searching, your Google search result snippet may be annotated with the names of the user's connections who've +1'd your page. If none of a user's connections has +1'd your page, your snippet may display the aggregate number of +1's your page has received.

The +1 button isn’t just for search results. We’re working on a +1 button that you can put on your pages too, making it easy for people to recommend your content on Google search without leaving your site.

Notes

The +1 button on a page can have a URL assigned to it that is different from the URL of the page where it resides. However, there is little benefit in having a +1 button pointing to a different page for the following reasons:

• the user will only be able to increment the URL score once (per user);
• clicking the +1 on different pages toggles the rating against the defined URL (i.e. it subtracts and adds alternately when clicked on different pages);
• the user may be confused and assume the button is related to the page where it is located.