Hummingbird is a Google algorithm released in 2013.
The Hummingbird update was the first major update to Google’s search algorithm since 2010. According to Gianluca Fiorelli, it is all about synonyms and context: this algorithm is capable to judge the intent behind a search and to determine what they are trying to find out.
Hummingbird is aimed at making interactions more human since it is capable of understanding the concepts and relationships between keywords. It places greater emphasis on page content making search results more relevant.
With Hummingbird, Google stepped officially in the domain of semantic search.