The first one, a bit of a sterile, clinical definition: https://en.wiktionary.org/wiki/normalcy_bias
The second goes into a bit more of a practical description: http://thesurvivalmom.com/normalcy-bias/
In my own words: it is a phenomenon that causes a person to reflexively REJECT information that is extremely troubling, dangerous, and worrisome. Rather than carefully analyze and attempt to develop a proper context for such information, an easier path is to just reject it out of hand!
Examples: "That can't be true, government would never allow it..." or "This is America, that can never happen here..."
:)