A title tag identifies a web page and tells both users and search engines what its content covers. Because it's one of the first details people notice in search results, and also what typically shows as the clickable blue link, it should be clear, informative, and genuinely relevant to the page rather than vague or generic.
Title tags have no hard character limit, but Google truncates display based on pixel width rather than character count, which means the safe practical range varies by which letters are used; keeping titles to roughly 50-60 characters is the more reliable way to avoid truncation than counting characters alone. Google also rewrites a meaningful share of title tags in results when it judges the written one doesn't match the query well, pulling from the page's headings or content instead, so a title genuinely reflecting the page's actual topic and search intent gets rewritten less often than a title stuffed with keywords or written for branding over clarity. The target keyword belongs in the title where it fits naturally, but the more reliable goal is a title someone would actually want to click, since that's what drives the click-through rate a title is really there to influence.
