Vestigial structures are those that used to serve a purpose, but through the process of evolution, no longer do. For example, an ostrich and an emu have wings, but they are no longer used for flying; the wings are vestigial. So are the human wisdom teeth.
One might think of vestigiality in matters beyond anatomy:
Many trauma victims have built up coping and protection mechanisms that used to get them through tough times, but once they’re through, they haven’t learnt to let go of them. Many overachievers have a hard time slowing down and enjoying life because constant overachieving is what got them to where they are now!
It pays to occasionally look at your life and think, does this serve a purpose anymore?
There are many more concepts in my "Mind Expander" tool (it's free)