Hreflang
Hreflang is an annotation that tells search engines the language and optional regional targeting of a page, so the correct version is served to the right audience. It is implemented via link tags, HTTP headers, or XML sitemap entries and requires reciprocal references.
Why It Matters
For multilingual or multi-regional sites, hreflang prevents the wrong-language page from appearing in results and reduces duplicate-content confusion between similar localized versions. Done right, it sends users to the version that fits their language and location.
Common Mistake
Non-reciprocal annotations where page A points to B but B does not point back, plus wrong language or region codes. Hreflang must use valid ISO codes and every referenced URL must return the same set of annotations, or engines ignore them.