Macro Lens at 150mm??

Hey everyone, I am really interested in Macro photography and I may be looking for a good Macro lens. I am using an Nikon D7000.

What I noticed was that some lens at 150mm and up were called Macro Lens...how can that be possible? Should macro lens have a focal range or around 50mm in order to get the 1:1 ratio?

Just how many types of Macro lens are out there?

If I use my 18-105mm VR lens, would the 18mm-around 75mm be considered "Macro"?

Thanks!