Google started testing ads in the Google app's Discover feed — then the Google Feed — around this time last year, with advertisements mixed in with non-sponsored content. The test wasn't popular; the proximity of the feed to many phones' home screens made the ads feel especially obtrusive. But it was apparently a hit with advertisers, as Google has announced that those ads will be the norm this year.
The bulk of feed ads will be part of two new advertisement categories Google is introducing called Discovery ads and Gallery ads. The new ad types will show up not only in Discover, but in places like YouTube, Google Images, and the Promotions and Social tabs of Gmail. You'll start seeing these ads throughout the year, as early as today. Existing ads are also worming their way into Discover.
The nomenclature is really only important for advertisers, though. For users, the takeaway is that we'll be seeing more ads in more places. That's unpleasant, but not surprising: Google is in the business of selling ad space in front of our eyeballs, after all.