grammar

A grammar is a structured way of explicitly capturing the normal implicit rules of natural language or defining the normative rules of an artificial one. Grammars are often based on non-terminal symbols (such as SENTENCE or NOUN_PHRASE) expressing phrases or logical groups of words and terminal symbols (often single words (such as 'dog'); grammar rules then express how non-terminal symbols expand into sequences of other non-terminal and terminal symbols. In natural language processing, grammars are often used to turn an input sentance or text into a parse tree.