R

Latin alphabet Aa Bb Cc Dd Ee Ff Gg Hh Ii Jj Kk Ll Mm Nn Oo Pp Qq Rr Ss Tt Uu Vv Ww Xx Yy Zz

R is the eighteenth letter of the Latin alphabet. Its name in English is ar [ɑːɹ].

Semitic Rêš (the head) developed into Greek Ρ ῥῶ (Rhô) and Latin R. The Latin and Etruscan forms of the letter added an extra stroke to distinguish it from a later form of the Greek Pi.

See rhotic consonant, r-colored vowel, and guttural R for discussion of the family of 'r' sounds.

In the International Phonetic Alphabet, 'r' represents the alveolar trill sound.

Miniscule

The miniscule (lower-case) form of r developed through several variations on the capital form. In handwriting it was common not to close the bottom of the loop but continue into the leg, saving an extra pen stroke. The loop-leg stroke shortened into the simple arc used today.

Another miniscule, the r rotunda, kept the loop-leg stroke but dropped the vertical stroke. It fell out of use around the 18th century.

Alternative representations

Romeo represents the letter R in the NATO phonetic alphabet.

In international Morse code the letter R is DitDahDit: · - ·

In Braille the letter R is represented as ⠗ (in Unicode), the dot pattern:

X.
XX
X.

Computing

In Unicode the capital R is codepoint U+0052 and the lowercase r is U+0072.

The ASCII code for capital R is 82 and for lowercase r is 114; or in binary 01010010 and 01110010, correspondingly.

The EBCDIC code for capital R is 217 and for lowercase r is 153.

The numeric character references in HTML and XML are "R" and "r" for upper and lower case respectively.

Meanings for R

• In architecture, R-value is a non-SI measure of thermal resistance used in housing insulation.
• In biochemistry, R is the symbol for arginine
• In calendars, R is often used as an abbreviation for Thursday instead of T, to avoid confusion with Tuesday
• In chemistry,
  • R denotes the gas constant
  • In organic chemistry, R (from German Rest) is the symbol for an unspecified hydrocarbon chain
  • In stereochemistry, R (rectus) signifies clockwise arrangement of substituents around a carbon atom using the Cahn Ingold Prelog priority rules
• In chess, R is a notation symbol for the rook piece
• In the RGB colour model, R stands for the colour red
• In commerce, R with an enclosing circle, ®, denotes a registered trademark
• In complexity theory, R is a commonly-used name for two complexity classes:
  • The class of recursive languages
  • The class of languages solvable in probabilistic polynomial-time with one-sided error, also called RP
• In computing,
  • R is the name of a statistical programming language based on S; see R programming language
  • r is sometimes used as the symbol for the rune 16-bit unit
• In driving a motor vehicle, R designates the reverse gear of a transmission
• In electrical engineering, R is often the variable for electrical resistance
• In film, R is a rating given for films given by film classification boards (such as the Motion Picture Association of America in the US), meaning "restricted"; see R (rating)
  • R is a character in the James Bond film The World Is Not Enough
• In finance, R is the U.S. ticker symbol for Ryder Systems Inc.
• In geometry, r is often a variable for the radius of a circle
• In law, the abbreviation R. or R stands for either Rex (King) or Regina (Queen) depending on who is sitting on the throne at the time. The title is mostly used by commonwealth countries in citing a criminal case to represent the prosecuting party (i.e. The Crown). In the United States, the term "United States" is usually used, or informally "the people" is sometimes used.
• In mathematics,
  • the symbol ℛ (script capital R, Unicode $211B) represents the Riemann integral
  • the symbol ℜ (black-letter capital R, Unicode $211C) represents the real part of a complex number
  • blackboard bold or ℝ (double-struck capital R, Unicode $211D) represents the set of all real numbers
• In music,
  • R, also known as Rated R is a Queens of the Stone Age album.
  • R., is an a 1998 album by R. Kelly
• In navigation, R denotes the relative direction "right"; see left and right
• In physics,
  • R is the symbol for roentgen, a unit of dosage of ionising radiation
  • °R or °Ra is the symbol for the Rankine degree
  • °R or °Ré is the symbol for the Réaumur degree
  • °R or °Rø is the symbol for the Rømer degree
  • r stands for revolution in units of measure of angular velocity such as the revolution per second (rps)
• As the first letter of a postal code,
  • In Canada, R stands for Manitoba.
• In radiocommunication, R is one of the ITU prefixes allocated to Russia
• In the romanization of the Japanese language, the letter R was selected instead of the letter L for the syllables in the tenth tier of the kana, for both the Hepburn system and the Kunrei, amongst others.
• In statistics,
  • R is the name of a statistical programming language based on S; see R programming language
  • r is the Pearson product-moment correlation coefficient
• In chemical engineering, r denotes the molar formation rate per volume (mol s^-1 m^-3)
• the 3 Rs (Reading, wRiting and aRithmetic)

Pronunciation of R

See also

• Raidô
• Я (Cyrillic Ya)