In short: Verizon, today, penned a blog post giving an update on its 5G network and also announced 5G Ultra Wideband. Millimeter wave spectrum is part of the 5G Ultra Wideband network, and Verizon says that through tests, it has discovered that high-frequency, ultra-wide millimeter wave delivers the best 5G experience to customers.
Background: There are essentially three pillars to a successful 5G network. This includes having massive spectrum holdings - especially in the millimeter wave bands, as it is the only spectrum available right now that has the potential for maximum capacity, throughput and latency. The other two pillars include end-to-end deep fiber resources (which Verizon has through its FiOS business), and the ability to deploy a large number of small cells. And this is what Verizon calls its "5G Ultra Wideband" technology. 5G in general is going to provide a ton of capacity and still have decent coverage, thanks to carriers using their low-band spectrum in conjunction with this high-band spectrum.
The impact: This isn't going to change how Verizon's 5G network works. It's still going to be 5G, and work just the same as a 5G network from Sprint, T-Mobile or AT&T. However, Verizon does have a ton of millimeter wave spectrum already, as well as high-band spectrum (near the 40GHz area) that is going to help Verizon offer way more capacity than other carriers. And that is what the carrier is really trying to highlight with the "5G Ultra Wideband" name here. Verizon has also been installing Small Cells for quite a few years, in an effort to densify its 4G LTE network. So that it already has a leg up when it comes to Small Cells as well, which is actually really important towards a 5G network, since you are relying more on more capacity spectrum rather than lower-band spectrum that offers more coverage.