The phrase "flagship device" refers to the top or most important product of a company. It's like the captain or leader of all their products. Full definition
As we push into 2016 the new wave of flagship devices come with formidable camera specs. (pocket-lint.com)
Basically, having a metal frame is a prerequisite for flagship devices in 2016. (bgr.com)
So in more ways than one, the One X + was more of a refined version of the original One X rather than an all - new flagship device from the manufacturer. (android.gs)