Stood for “Northern Rivers TV”, which is what the area from the QLD border down to about Grafton or so is known as, so made up maybe three-quarters of 11-8’s pre-aggregation coverage area (the colloquial “Port [Macquarie] to Southport” they mentioned in the news, apparently).
But in the 1990s after aggregation and having its viewing area extended to Gosford, I guess “NRTV” probably just stood for itself, much like so many empty acronyms these days. Little wonder why Ten/Telecasters decided to get rid of the name, and it probably helped that Southern Cross were of the same mind.