MaximumPC gets credit for this news article, see below for the source link. Basically Windows 10 will show ads on your lockscreen. I personally have not seen them yet but thanks to this article I disabled the option.
From the article on how to disable the ads:
...Hit the Start button, load the Settings app, choose Personalization, and then Lock Screen. Here you’ll see the Background field, which may already display the Windows Spotlight option by default; change this to Picture or Slideshow. Also disable “Get fun facts, tips, tricks, and more on your lock screen.”