What is Hreflang?

Google is informed of the language you are using on a certain page through the hreflang property, commonly known as rel="alternate" hreflang="x," so that users searching in that language can see that result.

An HTML feature called Hreflang is used to specify the language and location of a webpage. The hreflang tag can be used to inform search engines like Google about translations of the same page that exist in several languages. This enables them to provide their users with the right version.

Hreflang tags are a very useful snippet of code that you need to add to your website in case it is available in different languages or you have different store views for different countries.
Their main goal is to help Google show the right version of the website to users depending on their location.

If you want to have a deeper understanding of how hreflang tags work, I suggest you to read this article from Scandiweb, it really helped me clarify all my doubts about hreflang and canonical tags for international stores.