Terminals are endpoints in a syntax definition. No other resolution is possible. Terminals include the set of reserved words and user-defined identifiers.
Nonterminals are placeholders in the syntax. Most are defined elsewhere in this syntax summary. Definitions can be recursive. The following nonterminals are defined in the Grammar Summary of the C++ Language Reference:
constant, constant-expression, identifier, keyword, operator, punctuator
An optional component is indicated by the subscripted opt. For example, the following indicates an optional expression enclosed in curly braces:
{ expressionopt }