Hmm I'm not an expert here but IMO the wording is just marketing jargon. Most important thing is to look at the supported resolutions. Could be that "hd ready" supports 720p while hdtv is 1080p or more. Not really sure, but either way when looking at monitors, you should look at getting one that supports higher resolutions (1920x1080 is great), has 5ms response or better, and ideally a high contrast ratio like 40,000:1 or better.
It's not just marketing jargon; its a genuine difference.
Typically, "HD Ready" signifies 720p (true 720) or 1080i (interlaced).
While true HD displays have a native resolution of atleast 1080p (progressive).
The difference in 1080i & 1080p is the way image processing & rendering is done. Without going into the technical details, I'll just tell you that 1080p is better than 1080i, especially in fast moving images.