What is "the three rs"

R \R\ ([aum]r). R, the eighteenth letter of the English alphabet, is a vocal consonant. It is sometimes called a semivowel, and a liquid. See Guide to Pronunciation, [sect][sect] 178, 179, and 250-254. ``R is the dog's letter and hurreth in the sound.''
--B. Jonson.

Note: In words derived from the Greek language the letter h is generally written after r to represent the aspirated sound of the Greek "r, but does not affect the pronunciation of the English word, as rhapsody, rhetoric. [1913 Webster] The English letter derives its form from the Greek through the Latin, the Greek letter being derived from the Ph[oe]nician, which, it is believed, is ultimately of Egyptian origin. Etymologically, R is most closely related to l, s, and n; as in bandore, mandole; purple, L. purpura; E. chapter, F. chapitre, L. capitulum; E. was, were; hare, G. hase; E. order, F. ordre, L. ordo, ordinis; E. coffer, coffin.

The three Rs, a jocose expression for reading, (w)riting, and (a)rithmetic, -- the fundamentals of an education.

The three Rs (as in the letter R) refers to the foundations of a basic skills-oriented education program in schools: reading, writing and arithmetic'''. It appeared in print as a space-filler in "The Lady's Magazine" for 1818, although it is widely quoted as arising from a phrase coined in a toast given by Sir William Curtis, Member of Parliament, in about 1825. Since its original creation, many others have used the term to describe other trifecta.

The Three Rs (3Rs) in relation to science are guiding principles for more ethical use of animals in testing. They were first described by W. M. S. Russell and R. L. Burch in 1959. The 3Rs are:

1. Replacement:''' '''methods which avoid or replace the use of animals in research
2. Reduction: use of methods that enable researchers to obtain comparable levels of information from fewer animals, or to obtain more information from the same number of animals.
3. Refinement: use of methods that alleviate or minimize potential pain, suffering or distress, and enhance animal welfare for the animals used.

The 3Rs have a broader scope than simply encouraging alternatives to animal testing, but aim to improve animal welfare and scientific quality where the use of animals cannot be avoided. In many countries, these 3Rs are now explicit in legislation governing animal use.

It is usual to capitalise the first letter of each of the three 'R' principles (i.e. 'Replacement' rather than 'replacement') to avoid ambiguity and clarify reference to the 3Rs principles.