A title tag is the HTML element, written as <title> in the page head, that specifies the title of a web page. It appears in three important places: the browser tab, the bookmark label, and - most consequentially - as the large blue clickable headline in search engine results. Because of this visibility, the title tag is one of the most important on-page SEO elements.
Unlike the meta description, the title tag is a genuine ranking factor. Search engines weigh the words in the title heavily when matching a page to a query, and users decide whether to click largely based on it. A strong title accurately describes the page, includes the primary keyword near the front, and reads as a compelling, natural headline rather than a keyword list.
The effective length is bounded by pixels rather than characters, but a practical guideline is about 50 to 60 characters before search engines truncate the title with an ellipsis. Many sites also append a brand name after a separator, which is fine as long as the distinctive, keyword-rich part comes first and survives truncation.
Every indexable page should have a unique, descriptive title. Duplicate titles across pages confuse search engines and users about which page to show. Note that search engines sometimes rewrite titles they consider unhelpful, pulling from headings or other on-page text - another reason to make your title clear, accurate, and closely matched to the page's actual content.