The May Day Algorithm was a change made to Google's ranking algorithm.
Initially, it was viewed as a penalty. This was because the new change meant that some websites lost 90% of their traffic from Google for keyword phrases with long tail keywords (three or more keywords). One website affected by the new algorithm was a 13 year old site with a Google PageRank of 7 and 400,000 backlinks. Obviously this was a very well established website - so why did it begin to lose traffic?
Identifying keyword phrases requires a lot of computing power and a lot of memory. Before the new algorithm was introduced, Google says that it guessed the most appropriate pages for long keyword phrases based on other signals and keywords on the indexed pages. The new change in the algorithm has given Google the computing power to index long tail keywords on web pages more accurately, instead of using other simpler keywords on the page.
If words don't appear in the right order in keyword phrases, the web pages must be edited. The new algorithm will not get listed for a mixture of the keyword phrases - it will only get listed for the keyword phrase order that you've written.
So, is the May Day Algorithm a way of penalising websites, or will it boost websites' search performance in the long run?