Google makes thousands of updates to its algorithm every year now, with most being minor. The first major update was Fred, with the name itself being a joke, as Google did not announce an official name for it. Instead, Google’s Gary Illyes made a joke about calling all future updates “Fred,” and it stuck. Fred happened in March of 2017, and the focus was on sites that were either mainly ads or affiliate driven. It’s important to keep your content rich, and if you do allow ads on your site, not to overdo them.
There was actually a second confirmed update in the middle of December. If your site was using doorway pages or did not have Schema on it, chances are you saw a drop in rankings.