Blinkfeed, what exactly it is? HTC says best feature of the device. But what exactly is Blinkfeed?
BlinkFeed—an aggregator of news and social network content [...]
BlinkFeed will always occupy the leftmost page of the home screen.

The default BlinkFeed home screen of HTC Sense 5

(Wikipedia: HTC One)
To explain the second line:

By default, there will only be two home screen panels out of the box: a &quot;BlinkFeed&quot; page and a classic Android home screen on the right.

This explanation is taken from HTC One software hands-on: Sense 5, BlinkFeed, Sense TV and new Sync Manager (Engadget), where Blinkfeed is further described:

This is simply a Flipboard-like tile interface that sits permanently on the main home page. Created in collaboration with Mobiles Republic, this tool pulls in content from various publications and social networks (Twitter, Plurk, LinkedIn, Flickr, Zoe Share and more), as well as your calendar and TV shows from the TV app (more on that later). You won't be seeing emails here, as HTC positions BlinkFeed as a place for more ambient info rather than critical updates. Regardless, the feed can be customized to suit your needs, though the first version won't let you add custom RSS feeds just yet.

Read more in the linked articles themselves.