What are vestigial organs

These are 'useless' body-parts, otherwise known as vestigial organs, are remnants of lost functions that our ancestors possessed

Vestigiality is the retention during the process of evolution of genetically determined structures or attributes that have lost some or all of the ancestral function in a given species. Assessment of the vestigiality must generally rely on comparison with homologous features in related species.

there are so many examples for that in different areas, like biology experiment carried out in our lab recently.

here's one link: