Sponsored Content (aka native advertising) is "written stories, videos or podcasts that look and feel like journalistic content" (NYT).
Sponsored content is more than just advertising and it's meant to look like a legitimate part of the site. Though an online news source could be reputable, its sponsored content may not represent its values or, even worse, may be misleading and false.
Here is an example of the home page of the Financial Post business news from Canada. Note that these sponsored content examples are explicitly identified.