A log file is a record created by a web server that tracks how users and search engines interact with a website. It includes details like IP addresses, timestamps, requested URLs, response codes (like 200 for success or 404 for not found), and the types of browsers or bots making requests. By looking at these logs, SEO experts can see how often search engines visit their site, spot any crawling issues, check page load times, find broken links, and understand user behaviour—all of which helps improve visibility on search engines and boosts overall performance.