What are whale vestigial pelvic bones?
Whale is large tetrapod mammal with flipper like fore limbs but there is no hindlimb in body. Whales lost their hindlimbs during their evolution when they adapted completely to an aquatic life.
If we notice the body plan of vertebrates, it would be noted that girdles are bones which allow limbs to get attached to the axial skeleton. No hindlimbs means pelvic girdle bones are not anymore needed in whale.
The pelvic bones are still there in whale's body but in very ill-developed condition: so in whale pelvis is nonfunctional, or so to say it is vestigial.