It's tricky for Yahoo to communicate about how its business works, because Yahoo is the oldest and largest "portal" site, and so by design it tries to do (and milk revenue from) everything it can. Their business is complicated at a fundamental level by design, because sometime during the late 1990s, someone running Yahoo came to believe that the whole Internet was a kind of land grab, and the winner was going to be to the Internet what AOL was to, I don't know, the Internet for people who didn't know what the Internet was.
Since they're a huge public company, they have to communicate facts about their business to investors, with some precision, and so they expose you to terms like these.
A non-crazy way to think about Yahoo is like a magazine publisher that also owns a couple somewhat popular applications (mail, search). The "content verticals" are the magazines.