What is a ‘biscuit’ in US’ nuclear weapons launch process?

A “biscuit” contains the codes, known as Gold Codes, by which the US President can identify himself and authorise the use of nuclear weapons. A biscuit is about the size of a credit card. Recently, US President Joe Biden said the risk of nuclear ‘Armageddon’ is at the highest level since the 1962 Cuban Missile Crisis.