• J/K, jk : just kidding
• JASE : just another system error
• JC : Jesus Christ
• JCD : juris civilis doctor
• JCL : job control language
• JP : Justice of the Peace
• JSNM : just stark naked magic
• JUD : juris utriesque doctor, Doctor of Canon and Civil Law
• Ja River Warbler
• Jabalpur
• Jabiru
• Jack Snipe
• Jack-of-all-trades
• Jackal Buzzard
• Jackass Penguin
• Jackson's Akelat
• Jackson's Francolin
• Jackson's Hornbill
• Jackson's Pipit
• Jackson's Whydah
• Jacksonville
• Jacobian matrix
• Jacuzzi tm
• Jah slang
• Jaipur
• Jakarta
• Jamaica
• Jamaican
• Jamaican Band-tailed Pigeon
• Jamaican Becard
• Jamaican Blackbird
• Jamaican Crow
• Jamaican Euphonia
• Jamaican Lizard Cuckoo
• Jamaican Mango
• Jamaican Oriole
• Jamaican Owl
• Jamaican Tody
• Jamaican White-eyed Vireo
• Jamaican Woodpecker
• Jambu Fruit Dove
• James' Flamingo
• Jameson's Fire Finch
• Jameson's Wattle-eye
• Jamshedpur
• Jandaya Conure
• Jankowski's Bunting
• January
• Japan
• Japan finner
• Japanese
• Japanese Bush Warbler
• Japanese Cormorant
• Japanese Crested Ibis
• Japanese Green Pigeon
• Japanese Grey Bunting
• Japanese Grey Thrush
• Japanese Gull
• Japanese Hedge Sparrow
• Japanese Marsh Warbler
• Japanese Night Heron
• Japanese Pale-legged Willow Warbler
• Japanese Pied Wagtail
• Japanese Quail
• Japanese Reed Bunting
• Japanese Robin
• Japanese Snipe
• Japanese Sparrow Hawk
• Japanese Spotted Woodpecker
• Japanese Waxwing
• Japanese White-eye
• Japanese White-naped Crane
• Japanese Yellow Bunting
• Japanese beaked whale
• Japanese persimmon
• Japanese radish
• Japanese silk
• Java Ground Warbler
• Java Hawk Eagle
• Java Kingfisher
• Java Sparrow
• Javan Frogmouth
• Javan Grey-throated White-eye
• Javan Scops Owl
• Javan White-eye
• Javanese Collared Dove
• Javanese Fulvetta
• Javanese Mannikin
• Javanese Pond Heron
• Javanese Wattled Lapwing
• Jeepers creepers! coll.
• Jeepers!
• Jeez!
• Jeezem! coll.
• Jehovah's witness
• Jehovah's witnesses
• Jelski's Bush Tyrant
• Jelski's Chat Tyrant
• Jerdon's Babbler
• Jerdon's Baza