Hummingbird allows the Google search engine to better do its job through an improvement in semantic search. As conversational search becomes the norm, Hummingbird lends understanding to the intent and contextual meaning of terms used in a query
Hummingbird is about synonyms but also about context. Google always had synonyms, but with Hummingbird it is also able to judge context - thereby judging the intent of a person carrying out a search, to determine what they are trying to find out.