Short answer
An XML sitemap is a machine-readable list of the URLs a site wants crawled, usually with a last-modified date for each. It helps crawlers discover pages that internal linking reaches poorly, and it provides the freshness signal that tells a crawler which pages are worth revisiting.
Also called: Sitemap.xml
A sitemap does not guarantee indexing and does not improve ranking. Its practical value is discovery and recrawl prioritisation, which matters most for large sites, new sections, and pages that are several clicks from the homepage.
The quality problem to watch for is drift: URLs that no longer exist, pages excluded from the sitemap but still linked, and last-modified dates that update on every build regardless of whether content changed. Each teaches a crawler to trust the file less.
Related terms
robots.txt
robots.txt is a file at a site’s root that tells automated crawlers which paths they may request.
Structured Data (Schema Markup)
Structured data is machine-readable markup, usually JSON-LD following the schema.org vocabulary, that states explicitly what a page is about: that this string is a price, that one an opening time, this entity the organisation publishing the page.
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