Search logs are nothing but a mechanism search engines implement in order to give users absolute relevant results. It is a file (i.e., log) of the communications (i.e., transactions) between a system and the users of that system.
The use of data stored in transaction logs of Web search engines, Intranets, and Web sites can provide valuable insight into understanding the information-searching process of online searchers.
For Web searching, a search log is an electronic record of interactions that have occurred during a searching episode between a Web search engine and users searching for information on that Web search engine. Search log study actually began when the era of search engines on World Wide Web was initiated. As when the knowledge contents all over the world began to get consolidated over the internet, the study of search log interested many.
Talking about Google.com, the giant search engine and a world leader on the web, which gives you accurate results almost every time. So how’s that possible? Google, like any other search engine monitors or tracks user behavior and displays the results accordingly.
Let’s try to explain this concept in a simple way. When someone searches “cars” for example on Google, the search engine searches it over web and sends back the result in fraction of a second. Then what happens is they store some data about this exchange: the search query (“cars”), the time and date it was typed, the IP address and cookie of the computer it was entered from, and its browser type and operating system.
This user behavior in kept on user’s browser in form of cookies. A cookie (technically, an HTTP cookie) is a small file stored by your web browser. It looks like a lot of numbers, letters and symbols strung together. A cookie records user preferences. Using these cookies on their search logs, search engines optimize queries in best possible way. This information on your browsers also helps them to send you relevant ads. As you could see these days, they display ads to you which you may interest or you where looking for it earlier some time.
You can clear cookies any time on your browser through browser settings tab. There will be considerable difference in search results before and after deleting the cookies. The video explains the story.