Backus Naur Form

BNF is an acronym for "Backus Naur Form". Many extensions and variants of the original notation are in use; including Extended Backus–Naur Form (EBNF) and Augmented Backus–Naur Form (ABNF).

John Backus and Peter Naur initially introduced it - it allows you to ignore whitespace - allowing you to space out your code and not worry about 'spaces'.

The meta-symbols of BNF are:

::=	meaning "is defined as"
\|	meaning "or"
< >	angle brackets used to surround category names.