Why We Call it the "DS9/NEM division shirt"

We call this the "DS9/NEM division shirt" because, although it was first introduced in TNG's First Contact, the majority of the time this garment was in use and seen on screen (both in terms of longevity and production) was during the last two and a half seasons of Deep Space Nine. These garments underwent some experimentation and evolution, ultimately culminating in those seen in TNG's Nemesis, which we regard as the finalized, ideal versions. 

These garments, in addition to being an integral component to every standard Starfleet DS9/NEM duty uniform, also indicated the division of the wearer. 

Hence why we call it the "DS9/NEM division shirt!" 

Now, onto an analysis of the garment itself!

NEXT: Analysis, part 1 - Division Colors