This term refers to a state of matter that is the opposite (or alternative) of hadronic - where hadronic is any normal state of matter where there are heavy particles, which are essentially groups of quarks. Subhadronic is apparently a phase of matter that inverts, leaving empty space and creating a lot of energy and heat (as in the collapsing of the center of a star). http://www.technologyreview.com/blog/arxiv/23677/
I've researched this, and found very little on the word. If anyone can add more or clarify exactly what Subhadronic means, I would love to learn about it!