• R&D
• R4L
• R4YL : Run for life!
• RAC : Royal Automobile Club Br.
• RAEBNC : Read and enjoyed, but no comment
• RAF : Royal Air Force
• RAID : Redundant Array of Independent/Inexpensive Disks
• RC : Roman Catholic
• REHI : Hi again!
• REM sleep
• RFC : Request for comments
• RFD : request for discussion
• RL : real life
• RN : Royal Navy
• ROFL, ROTFL : rolling on the floor laughing
• ROTFLACGU : rolling on the floor laughing and can't get up
• ROTFLAHMS : rolling on the floor laughing and holding my sides
• ROTFLBTC : rolling on the floor laughing biting the carpet
• ROTFLGO : rolling on the floor laughing guts out
• ROTFLMAO : rolling on the floor laughing my ass off
• ROTFLSHIWMP : rolling on the floor laughing so hard I wet my pants
• RP : reply paid
• RPM-regulated
• RR : railroad Am.
• RS : Royal Society Br.
• RSN : real soon now
• RSPCA : Royal Society for the Prevention of Cruelty of Animals
• RSVP : repondez s'il vous plait, please reply
• RTFAQ : Read the frequently asked questions list!
• RTFM : Read the fine manual!
• RTFMA : Read the fine manual again!
• RTM : Read the manual!
• RTOH : Read the online-help!
• RTRT : realtime raytracing
• RV
• Rabat
• Rachel's Malimbe
• Racquet-tailed Coquette
• Racquet-tailed Roller
• Rad-faced Barbet
• Radde's Accentor
• Radde's Warbler
• Radio in the American Sector
• Radjah Shelduck
• Raffles' Malcoha
• Raggiana Bird of Paradise
• Raimondi's Yellow Finch
• Rain Quail
• Rain fell in sheets.
• Rainbow Lory
• Rainbow Pitta
• Rainbow Starfrontlet
• Rainbow-bearded Thornbill
• Rajah Scops Owl
• Raleigh
• Ramstein
• Rand's Red-billed Helmet Shrike
• Rangoon
• Rank nonsense!
• Rapa I Fruit Dove
• Rapunzel
• Rarotonga Flycatcher
• Rarotonga Starling
• Rarotongan Fruit Dove
• Ratchet-tailed Treepie
• Rats!
• Rattling Cisticola
• Rawalpindi
• Rayleigh quotient
• Rayleigh-scattering
• Raynaud's phenomenon
• Raza Island Lark
• Razor-billed Curassow
• Razorbill
• Rd : Road
• Re : reply
• Read it off!
• Ready, set, go! Am.
• Ready, steady, go! Br.
• Recife
• Recurvebill Brushbird
• Red
• Red & Black Grosbeak
• Red & Blue Lory
• Red & White Crake
• Red & White Spinetail
• Red & Yellow Barbet
• Red Bird of Paradise
• Red Bishop
• Red Cross
• Red Crossbill
• Red Flamingo
• Red Forest Fody
• Red Goshawk
• Red Honeyeater
• Red Jungle-fowl
• Red Kite
• Red Knot
• Red Lark
• Red Lory