Google on its 15th birthday announced the Hummingbird algorithm here are some key points to quickly understand it.
The world biggest search engine now more focus on understanding relationships among things phrase match meanings as you type or give instruction by voice as previously to its original strategy of matching keywords.
The Hummingbird algorithm will first understand the meaning of phrases in a query and display search pages that accurately match that meaning.
It is more related to Keyword Graph as announced by Google last year that understand the meanings of and relationships between things, people and places known as semantic search.
The algorithm also developed on the work Google has done to understand conversational language, like interpreting pronunciation in the search query refers to.