Mobile Connectivity is the strength of your mobile network when browsing the mobile web.
Mobile connectivity is important for page load speed, as users need to be able to access mobile content from a variety of mobile connection speeds.
Also, when targeting international audiences it is important to consider the average mobile-connectivity level in order to ensure you offer their webpages with the best possible user experience.
Typical connections include 5G, 4G & 3G, with WebPageTest.org offering tests for pages using 4G & a variety of Fast, Regular & Slow 3G.