There are two answers to this question.
The first is that the Pacific trash vortex is a humongous floating patch of litter which collects in the Northern Pacific Gyre. An endlessly swirling mass of plastic waste twice the size of the continental United States, testament to humanity’s decadence and disregard for the oceans which sustain us.
Is it real? Well, that’s another matter. The inestimable Brian Dunning addresses this question elsewhere.
The second is that the Pacific trash vortex is my blog-thing. My official blog-thing. The only blog-thing endorsed personally by me. Why call it the Pacific trash vortex? It could be seen as a metaphor. The churning quagmire representing the maelstrom of thought and ideas that is my mind.
However, unlike that most deceptively named of oceans, perhaps I am not very deep and just thought it sounded cool.