Server Logs: Server logs are files on a server that show the amount of traffic a website is getting, in addition to the sources of the traffic. These logs record the actions performed by any computer with access to the server, similar to the "history" log on a web browser. The log is usually only accessible to the server's webmaster.
While a server log typically records less data and is less user-friendly than analytics software, these logs still hold information regarding IP address, date and time of the request, HTTP code, number of bytes served, the page requested and more.
Webmasters can also use a server log as a way to monitor the search engine queries that are entered if a user links to the site via a search engine, making them an important resource for any SEO campaign. Server logs can even reveal the amount of time a user spends on each page -- an important measurement to monitor when trying to improve the efficacy of a landing page -- and reveal the "path" the user took when navigating around your website.
When used as part of an SEO campaign, the information that a server log can reveal is crucial to measuring the engagement of your website's audience.