Definition: So what are riblets and rib tips? These names have become
interchangeable, but they are different cuts of meat.

Rib tips are actually the very end (underside) of a rack of ribs. When a
rack is trimmed to make St. Louis style ribs there is a thin strip of
rib ends (or tips) left behind.

Riblets are cut from back or spare ribs to straighten them out. Even
notice how back ribs are rectangularly shaped? This is done by trimming
the bones to make them straight. Largely this is done for presentation.
There is something called rib buttons. These are not ribs, but back bone
cuts.

Source: http://bbq.about.com/cs/ribs/a/aa092003a.htm

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