What exactly is a Kidney Transplant? Why is it needed?

The links and video below give in-depth information describing what's a kidney transplant and why it is the preferred/needed course of treatment for those with kidney failure:

http://www.nhs.uk/Conditions/Kidney-transplant/Pages/Introduction.aspx

https://health.clevelandclinic.org/2014/07/4-facts-you-need-to-know-about-kidney-transplants-and-dialysis/

https://www.kidney.org/news/newsroom/factsheets/Organ-Donation-and-Transplantation-Stats

http://www.americantransplantfoundation.org/about-transplant/facts-and-myths/

http://www.hopkinsmedicine.org/healthlibrary/test_procedures/urology/kidney_transplantation_procedure_92,p07708/