A grammar school is a type of school found in some English-speaking countries. Its original intent was to educate the young in the grammar of one or two European languages. Grammar schools date back to earlier than the 16th century.
In the British case, that originally meant Latin and sometimes Greek in addition; and in the American case, that of English. However, the meaning of the term has since changed considerably, and grammar schools now provide as broad an education as any other type of school.
In the United States, the term has often been used as a synonym for primary school, although this usage is now at least somewhat in decline.
See secondary education, Grammar schools in the United Kingdom, Education in the United Kingdom, UK topics.