Yeah I think you may have got Marrow bones which are thicker bones with meat attached like these
RMB is short for "Raw Meaty Bones" which can consists as necks, backs etc. Any form of part that has bone in it that can easily be consumed. The marrow bones are more dense and hard, yet provide recreational chew because the bones themselves are too hard to swallow and digest unlike the smaller flexable bones of neck or back.
For good reading on raw and RMB I am pretty fond of this site.
www.rawdogranch.com more specific talk about RMBs can be found here - http://www.rawdogranch.com/rawmeatybones.htm

RMB is short for "Raw Meaty Bones" which can consists as necks, backs etc. Any form of part that has bone in it that can easily be consumed. The marrow bones are more dense and hard, yet provide recreational chew because the bones themselves are too hard to swallow and digest unlike the smaller flexable bones of neck or back.
For good reading on raw and RMB I am pretty fond of this site.
www.rawdogranch.com more specific talk about RMBs can be found here - http://www.rawdogranch.com/rawmeatybones.htm