Question: What is the "changefreq" tag in a sitemap and how can it be used?

The changefreq tag is an element in the XML Sitemap protocol used to provide a hint to search engines about how frequently they can expect a page's content to change. It's important to note that Google has stated they don't consider changefreq for crawl rate.

Values of changefreq can be: always, hourly, daily, weekly, monthly, yearly, or never. These values are indicative and not binding for search engines.

The syntax for including changefreq in a sitemap is as follows:

<url>
    <loc>http://www.example.com/</loc>
    <changefreq>daily</changefreq>
</url>

In this XML snippet, the URL http://www.example.com/ is expected to change daily according to the changefreq value.

Despite its limited use, some SEO professionals still recommend providing changefreq as it gives a complete picture of your website's update frequency even if it doesn't directly impact crawling.