Explain in simple terms what is Google's hreflang attribute?

Question

Google

Is it just markup to make it easier for Google to index the site?
https://support.google.com/webmasters/answer/189077

Answer 1

If your site is in one language, then you don’t need to bother with this issue. This is necessary if there are several versions of the site in different languages. As a rule, the texts for all versions are the same, so that search engines know about this and this attribute is needed. It is necessary to register on each page a link to the same page, but in a different language. There are examples and a description on the page you linked to in the question.