When Google started out, it had a database of indexed pages searchable by keywords and advanced search operators such as site:. Gradually, Google began adding semantic search features. (It has been reworking its storage, Index, accordingly, to contain “knowledge” type of data about stored pages). Here are the most significant semantic-oriented additions over the years.
A while ago, Google started searching for words with the same root (“auto-stemming”). About five years ago, we also started seeing keyword synonyms in the results. In recent years, Google has started showing featured previews and Knowledge Graph objects, in addition to search results.