Short answers, pulled from the story.
Grammar is the system of rules that governs how a natural language is structured and used, as evidenced by its speakers or writers. These rules may concern the use of clauses, phrases, and words. The term can also refer to the study of such rules, which includes phonology, morphology, syntax, phonetics, semantics, and pragmatics.
The word grammar derives from the Greek γραμματικὴ τέχνη, grammatikḕ téchnē, meaning art of letters. It comes from γράμμα, grámma, letter, which itself comes from γράφειν, gráphein, to draw or to write. The same Greek root also appears in the words graphics, grapheme, and photograph.
The ancient Greek scholar Dionysius Thrax, active around 170, wrote the oldest known grammar handbook, titled the Art of Grammar. He was a student of Aristarchus of Samothrace, and his book remained the primary grammar textbook for Greek schoolboys until as late as the twelfth century AD.
Descriptive grammar describes the grammatical constructions of a particular speech type in great detail, while linguistic prescription is a plan to marginalize some constructions and codify others. Linguists tend to view prescriptive grammar as having little justification beyond its authors' aesthetic tastes. The rules taught in schools are prescriptive in intent rather than descriptive.
Syntax refers to linguistic structure above the word level, such as how sentences are formed, while morphology refers to structure at and below the word level, such as how compound words are formed. No clear line can be drawn between syntax and morphology. Analytic languages such as Chinese and Afrikaans rely on syntax, while synthetic languages such as Latin rely on inflection.
National Grammar Day falls on the 4th of March. In the United States, the Society for the Promotion of Good Grammar designated the date as National Grammar Day in 2008.
The first systematic grammar of Sanskrit originated in Iron Age India, with figures including Yaska in the 6th century BC and Pāṇini in the 6th to 5th century BC. Tolkāppiyam, the earliest Tamil grammar, is mostly dated to before the 5th century AD, and the grammar of Irish originated in the 7th century with Auraicept na n-Éces.