Let’s take a look at the location for most of the game-play in Star Trek: BorderlandsOur game takes place in the 25 century in the Delta Quadrant of the galaxy. The current year is 2416. 

BL Map 0812R Moore

Federation colonization of the Delta Quadrant has left Starfleet overtaxed and overextended. The newly-formed Delta Freedom Alliance vies with the Federation for the hearts and minds of the Delta Quadrant denizens, and numerous criminal and terrorist factions have set up shop in this wild and lawless region of space. There are also colonies and ships of the Romulan Star Empire in the Delta Quadrant.   Additionally, a split in the Klingon High Council has deposited a vanguard fleet here, intent on proving the viability of a Klingon Territory.

The four factions mentioned make up the major powers dealt with in Star Trek: Borderlands play. 
You will notice from the map (top), that the Federation has most of the colonized space. Starbase Horizon, Outpost Hope One, and Starbase Phoenix are easily located with the blue section representing Federation Space. 
As you can see, we are right at the outer edge of the territories dealt with in the series Star Trek: Voyager. This is previously unknown space made accessible by the Genosh Wormhole.
Our crews face the unknown on a regular basis, but they must also deal with the same old Alpha Quadrant politics as they eke out their existence and explore this vast new frontier. 
This is why we call it Borderlands.