Symbols in this system are surrounded by angle braces, and ::= (colon-colon-equals) is used for "is defined as".  
Messages are a fundamental component of a variant of this thing created for use in routing by Farrel.  Another variant, RFC 5234, adds elements such as incremental alternatives to it. Donald Knuth is credited with removing the word "normal" from the name of this system. The initial version of this thing was proposed at a UNESCO conference by an IBM engineer working on ALGOL 58. Niklaus Wirth tackled the "unnecessary diversity" in this system by adding an explicit iteration construct, basing it on ASCII, and not using a symbol for empty strings. Wirth proposed the (*) "extended" form of it. A variant of this system is used to specify the "rules" parameter passed to yacc. Symbols in this system are surrounded by angle braces, and ::= (colon-colon-equals) is used for "is defined as".  For 10 points, name this doubly eponymous notation system for a context-free grammar.
Messages are a fundamental component of a variant of this thing created for use in routing by Farrel.  
Backus-Naur form [or Backus normal form; or Backus-Naur notation; or BNF; or Extended BNF; or Augmented BNF; or Routing BNF] 