What is "three rs"

1824; said to have been given as a toast by Sir William Curtis (1752-1829), a beloved lord mayor of London in the 1820s, who seems to have been a figure of fun to whom many mangled phrases were attributed. Among the toasts he is alleged to have given at public dinners were "The Female Ladies of London;" "The three C's
--Cox, King, and Curtis;" and "The three R's
--Reading, Writing, and Rithmetic."\n\nIt has been very much the fashion amongst a class of persons to attribute to Sir W. C. ... a vulgarity and ignorance of speech which are by no means consistent with his character and conduct. The worthy and hospitable baronet has a rapid mode of speech, but it is always correct ; and although some eccentricities are mixed up in his composition, he is highly honourable, and has been a very useful member of society, particularly to his London constituents.

["The Mirror," Jan. 29, 1825]

\nAfter listing some examples, the article continues:\n\nIt is, however, very certain, that at a city festival some years ago, having indulged very freely, he fell asleep, when some wag, choosing to consider him dead, wrote his epitaph, which was found next morning pinned to the baronet's dress coat:
--\n

"Here lies the great Curtis,\n
Of London, Lord May'r:\n
He's left this here world,\n
And gone to that there."\n \n

n. 1 The basic education received in primary schools. Literally; reading, writing and arithmetic. 2 The basic education any child can expect to receive, but not necessarily limited to reading, writing and arithmetic. 3 (context idiomatic English) The basic precepts of any subject matter.