The holiday of Passover was named Pesach in Hebrew since the word translates to "Passing Over."
When the 10 plagues were thrown upon the Egyptians, the last plague, "The Slaying of the First Born," was directed only to the Egyptians. Pharaoh's first born son was killed when G-d commanded this order.
For the plague to not kill the Jewish first born males, the Jews took the shankbone's blood and spread it on their doorpost. This allowed the Jewish homes to be passed over.