What exactly is "grammar", please give me details!
And an other dictionary says;

The study of words and of the rules for their formation and their relationships to each other in sentences.
Here is what the dictionary has to say:

Main Entry: gram·mar
Pronunciation: 'gra-m&r
Function: noun
Etymology: Middle English gramere, from Middle French gramaire, modification of Latin grammatica, from Greek grammatikE, from feminine of grammatikos of letters, from grammat-, gramma -- more at GRAM
Date: 14th century
1 a : the study of the classes of words, their inflections, and their functions and relations in the sentence b : a study of what is to be preferred and what avoided in inflection and syntax
2 a : the characteristic system of inflections and syntax of a language b : a system of rules that defines the grammatical structure of a language
3 a : a grammar textbook b : speech or writing evaluated according to its conformity to grammatical rules
4 : the principles or rules of an art, science, or technique
- gram·mar·i·an /gr&-'mer-E-&n, -'mar-/ noun

(From Merriam-Webster's online site, [url="
http://www.m-w.com "]www.m-w.com[/url].
 Mike in Japan's reply was promoted to an answer.