From IFWiki

The set of all verbs and sentence structures that a game understands. In most languages, grammar is defined with separate grammar elements, each element being either something like "the verb 'take', which can be followed by a list of objects" or something like "a list of objects consists of one or more objects with the word 'and' or a comma in between each." The game's grammar is generally not considered to include the nouns and adjectives that refer to the physical objects in the game: those are held in the game's dictionary. (DS)