Help is at hand for those perptually confused when confronted by terms such as op. cit., ibid., and Q.E.D., not to mention the millions of people who use i.e. and ad lib without knowing their true meaning.

AD - anno Domini (in the year of the Lord)
ad lib. - ad libitum (at pleasure)
a.m. - ante meridiem (before noon)
c. - circa (about)
et al. - at alii (and others)
etc. - et cetera (and so on)
ex lib. - ex libris (from the books of)
ibid. - ibidem (in the same place)
i.e. - id est (that is)
N.B. - nota bene (note well)
ob. - obiit (died)
op. - opus (work)
op. cit. - opere citato (in the work cited)
p.m. - post meridiem (after noon)
p.s. - post scriptum (post script)
Q.E.D. - quod erat demonstrandum (which was to be demonstrated)
R.I.P. - requiescat in pace (rest in peace)
viz. - videlict (that is to say)