The Hummingbird update was different from the major algorithm updates like Penguin and Panda, revising core aspects of how Google understands what it finds on the pages it crawls. In today's Whiteboard Friday, Rand explains what effect that has on long-tail searches, and how those continue to evolve.
Now long tail, if you're not familiar already, is those queries that are usually lengthier in terms of number of words in the phrase and refer to more specific kinds of queries than the sort of head of the demand curve, which would be shorter queries, many more people performing them, and, generally speaking, the ones that in our profession, especially in the SEO world, the ones that we tend to care about. So those are the shorter phrases, the head of the demand curve, or the chunky middle of the demand curve versus the long tail. 

How Google is Changing Long-Tail Search with Efforts Like Hummingbird - Whiteboard Friday