Abbreviations and Acronyms:  J - R

lat. 

From latitude.

lc

From Latin loco citato, meaning "in the place cited."

long.

From longitude.

K

From Kelvin.

M.O.

From Latin modus operandi, meaning "method of operating."  M.O. often refers to a criminal's methods.

n.b.

From Latin nota bene, meaning "mark well."  N.b. draws attention to material, asking the reader to "please note" or "note well" this information.

op. cit.

From Latin opere citato, meaning "in the work that was cited."  Op. cit. refers again to the last work cited.  Op. laud., from opere laudato, functions equivalently.

p.m.

From Latin Post Meridiem, meaning "after midday."

p.m.a.

From Latin post mortem auctoris, meaning "after the author's death."

pop.

From population.

P.S.

From Latin post scriptum, meaning "after writing."  A postscript is writing added after the body of a letter.

pseud.

From pseudonym.

pub.

From published or publisher.

Q.E.D.

From Latin quod erat demonstratum, meaning "which was to be demonstrated."  Q.E.D. is often cited at the end of a mathematical proof.

q.v.

From Latin quod vide, meaning "which see."  Q.v. follows a term or phrase that should be explained elsewhere in the text.  The plural form is qq.v., quae vide.

re or Re:

From Latin res, meaning "[in] the matter of" (literally "by the thing").  In English usage, re means "about" or "concerning."  In correspondence, especially in e-mail replies, Re: is often mistaken for an abbreviation of "regarding" or "reply," which it is not, though English usage assigns a similar meaning. 

rev.

From revised.

R.I.P.

From Latin requiescat in pace or requiescant in pace, meaning "may she / he rest in peace" or "may they rest in peace." 

R.S.V.P.

From French repondez s'il vous plait, meaning "respond if you please."  R.S.V.P. usually requests that the recipient of an invitation confirm or decline attendance.