I am not sure of the actual definition, but I know it means more then widescreen. I have an HDTV, but I also have TiVo. Tivo doesn't support HDTV currently, so my TV is not being used to it's potential.

As for the 1000 lines bit, my TV supports something like 1080 lines interlaced. If I'm not mistaken, this is very high and most US HD broadcasts are in 480 lines progressive (or somehting in that range). There is talk of the HDTV spec being abandoned, so who knows if I'll ever see my TV display anything by NTSC.

PS- Check out this site for video captures of US HDTV signals from various networks.

EDIT: After looking around (instead of talking out my ass), it seems HDTV is considered 1080i or 720p. NTSC is 480i. Fox doesn't conform to HighDef and broadcasts it's "digital" content in 480p. That's where I got confused.