Google Instant is a new search enhancement that shows results as soon as you type. In other word, it will "search" before you type. This is the internet search accelerator by adding a feature that displays results as soon as people begin typing.
As a user starts to type a search, Google Instant automatically shows results for a popular search that begins with those letters. An algorithm tries to predict what the rest of the query might be based on popular queries typed by other users. The predicted text is shown in light grey in the search box, and search results and ads are automatically shown for that predicted query.
Search results will now be shown for a new "predicted query". For example, if someone types "yo" into Google, an algorithm predicts that the user is searching for "youtube", “”yosemite national park”, etc (the predicted query) and therefore displays search listings and ads for “yo”. Those results will continue to show unless the next letters that the user types lead to a different predicted query. Neither click search nor press enter needed, the search result will be automatically updated.
Faster Searches: By predicting your search and showing results before you finish typing; Google Instant can save 2-5 seconds per search.
Smarter Predictions: Even when you don’t know exactly what you’re looking for, predictions help guide your search. The top prediction is shown in grey text directly in the search box, so you can stop typing as soon as you see what you need.
Instant Results: Start typing and results appear right before your eyes. Until now, you had to type a full search term, hit return, and hope for the right results. Now results appear instantly as you type, helping you see where you’re headed, every step of the way.
Today, Google Instant is starting to roll-out to users on Google.com domains in the US, UK, France, Germany, Italy, Spain and Russia who use the following browsers: Chrome v5/6, Firefox v3, Safari v5 for Mac and Internet Explorer v8. Users on domains other than Google.com can only access Google Instant if they are signed in to a Google Account. "We will continue to add new domains and languages over the next several months", Google said..
How To turn your Instan on or off?
If you don't want to see results as you type, you can turn off Google Instant by clicking the link next to the search box on any search results page, or by visiting your google preference :