Grammar
A grammar specifies the legal syntax of a language. The kind of grammar most commonly used in computer language processing is a context-free grammar. A grammar specifies a set of productions; non-terminal symbols (phrase names or parts of speech) are enclosed in angle brackets. Each production specifies how a nonterminal symbol may be replaced by a string of terminal or nonterminal symbols, e.g., a Sentence is composed of a Noun Phrase followed by a Verb Phrase.
<S> --> <NP> <VP> <NP> --> <ART> <ADJ> <NOUN> <NP> --> <ART> <NOUN> <NP> --> <ART> <NOUN> <PP> <VP> --> <VERB> <NP> <VP> --> <VERB> <NP> <PP> <PP> --> <PREP> <NP> <ART> --> A | AN | THE <NOUN> --> BOY | DOG | LEG | PORCH <ADJ> --> BIG <VERB> --> BIT <PREP> --> ON