Algorithm update (Google algorithm update)
Any change to Google’s search algorithms or ranking system. This includes new rules or adjustments to rules already in place. There are frequent small updates that go unnoticed, but there are several major updates in a year that can have a big impact on your rank.
Major updates in the past few years include Panda, Penguin, Pirate, Hummingbird, Pigeon, Mobile Friendly, RankBrain, Possum and Fred.