From setiquest wiki
The galactic anticenter is a theoretical point in the sky that lies directly opposite the center of the Milky Way galaxy (the galactic center). Because this point is relative, it will vary depending on the location of the observer; it is not an actual fixed point in space. Within the context of setiQuest, however, this term generally refers to the anticenter from the point of view of an observer on Earth.
The motivation for studying the galactic anticenter in SETI is the hypothesis that the galactic center is one of a few points in space that can be argued to have special significance for all civilizations in the galaxy. It is plausible, then, that a transmitting civilization would transmit towards the galactic center as seen from their location rather than towards other, arbitrary points in space for which no special significance can be inferred.
For the vast majority of possible transmitting locations in the galaxy, we would not be able to intercept such transmissions on the Earth, since we are not positioned on the same line-of-sight as the galactic center as seen from the transmitter's location. There is one exception, though, and that is locations lying on or close to the line originating from our position and extending towards the position of the galactic anticenter. Any signals emitted towards the galactic center by transmitters along this line will also pass the Earth.