It could mean:.
Reference range, in laboratory medicine. .
Relative risk, in statistics and epidemiology .
Respiratory rate, as a vital sign .
Rhesus factor, in immunohema…tology. .
Chip 'n Dale Rescue Rangers, an animated TV series .
Rainbow Road, a course in the Mario Kart series .
Reading Rainbow, an American children's television program .
Rickrolling, an internet meme .
Ricky Ricotta, a children's book series by Dav Pilkey .
Road Rules, a reality series on MTV .
Rocka Rolla, heavy metal album by Judas Priest .
Royal Rumble, annual WWE pay-per-view .
Rockin' Robin .
Rachael Ray, an American television personality .
Ronald Reagan, 40th President of the United States of America .
Robert Reiner, actor .
Rick Robertson, AKA Double R, Seattle radio personality .
Rajasthan Royals, an Indian Premier League franchise .
Rashtriya Rifles, Indian counter-insurgency force .
Reach Records, a Christian hip hop record label .
Red Rooster, an Australian fast food chain .
Rekords Rekords, an American record label founded by Josh Homme .
Road Runner (ISP) .
Royal Air Force, IATA airline designator .
Rational Recovery .
RR layout, Rear-engine, rear-wheel drive layout, in automotive terminology .
Request-response, a synchronous messaging model commonly used in distributed computer systems .
Resource records used in Domain Name System (DNS). .
Riva Rocci, an abbreviation for blood pressure measured with a specific sphygmomanometer .
Round-robin scheduling .
Rapid Ride, a bus rapid transit system in Albuquerque, New Mexico .
Regional Railways, a former sector of British Rail .
Regional Roads in Ontario, a class of roads maintained by regional municipalities in Ontario (see County roads in Ontario) .
Royal Road, an ancient highway reorganized and rebuilt by the Persian king Darius I .
rr (digraph) .
Reader Rabbit .
Repurchase agreement rate (or repo rate; as in the Reuters Instrument Code US10YT=RR) .
Revised Romanization of Korean .
Rio Rancho, New Mexico .
Rolls-Royce (disambiguation) .
Roman Republic .
Rural route .
Russian ruble .
If you meant R & R, it probably means either "rest and rehabilitation" (military sense) or "rest and recreation". ( Full Answer )