A subspace node was a "bubble" of curved spacetime, resulting in an area of space devoid of any stars or other stellar bodies.
One such node was a region known as "the Barrens," wherein no star systems existed within one hundred light years. In the 22nd century, Emory Erickson, inventor of the transporter, utilized this area as a testing ground for his design of a sub-quantum transporter. (ENT: "Daedalus")