Noun
true rib (plural true ribs)
A rib attached to the spine and sternum, as opposed to a floating rib.
In humans the second rib is defined as a true rib since it connects with the sternum through the intervention of the costal cartilage anteriorly (at the front). Source: Internet
The phrase true rib ( Latin costae verae main), or fixed rib, refers to the first seven, or vertebrosternal, rib pairs. Source: Internet