HDTV channels are defined as <ch #>-1 or <ch #>-2. What do the -1 and -2 mean?

Answer 1

-1, -2, ... are the subbands of the given digital channel. -1 is typically a simulcast of its sister analog channel. -2 and above contain secondary programming that the digital channel holder wishes to provide.

So far, I've noticed that the commercial network affiliates (ABC, CBS, NBC, FOX) will put 24-hr weather info on the subbands. The local PBS station here has 4 different PBS feeds on the same channel.

This is one of the by-products of the conversion from analog to digital: the licenseholders have the option of using the entire channel for HDTV, employ multicasting through subbands on a single channel, or a combination of both.