what is the grammar

Here's the short answer: when people talk about grammar, they usually mean the system of rules that decides how words change their form and combine into sentences in a language. This is how a learner's dictionary defines it: grammar is "the rules about how words change their form and combine with other words to make sentences." So grammar isn't a list of vocabulary or a set of tricky words to memorize. It's the underlying system that tells you things like: in English, you usually add -s to a verb when the subject is third-person singular (so you say she walks, not she walk), and that word order matters, so the dog bit the man means something quite different from the man bit the dog, even though the words are the same. A second, less common meaning: grammar can also refer to an actual book of grammar rules, as in "I bought a German grammar." That sense is marked as mainly British English. But in everyday speech, when someone says "your grammar is good" or "the grammar of this language," they're talking about the rule system itself, not a book. Quick check: In the sentence She walks every day, which part shows grammar at work? - good_result: The -s on walks. Right, that ending is grammar changing a word's form to show who is doing the action. - wrong_result: The word every. Not quite, that word adds meaning on its own; grammar is the system of rules for how words change form and combine, and it's the -s on walks that shows a rule in action. Destination: For a deeper look at how grammar differs from vocabulary, see the entry on "the difference between grammar and vocabulary."