Mobile-first indexing refers to the use of mobile versions of webpages (rather than their desktop alternative) to index and rank URLs. This practice has been adopted by Google in recognition that the majority of their users access the search engine via a mobile device rather than a desktop.
Those websites that have not optimised their content for mobile display, or who have not built out a mobile display alternative, will experience a demotion in Google’s ranking system when the mobile-first index is used. Regardless of the index, Google’s intervention to create mobile-first indexing shows that the majority of web users will access websites using their phones, not their computers and this should be considered when creating one.
