What does 'b.c.' mean in the description of a Bach Quintet in D Major
for flute, oboe, violin, viola and b.c.?

Dear millhill-ga 

BC is an abbreviation for basso continuo.

Classical abbreviations -
http://www.classicalarchives.com/bios/codm/abbr.html

Sources of J.S. Bach's Works
?Basso Continuo, B.c., Thorough-bass ?
http://www.bach.gwdg.de/instrum_eng_neu.htm#Continuo

?basso continuo (It.). Continuous bass. Figured bass from which in
concerted mus. of the 17th and 18th cents. the cembalist or organist
played. Doubled the lowest v. part. Term often shortened to continuo.
To ?play the continuo? does not mean to play a particular instr., but
to play this variety of bass.?
http://www.classicalarchives.com/dict/basso_continuo.html

?Basso continuo
Basso continuo parts, almost universal in the Baroque era (1600-1750),
were, as the name implies, played continuously throughout a piece,
providing the harmonic structure of the music. The word is often
shortened to continuo, and the instrumentalists playing the continuo
part, if more than one, are called the continuo group.?
http://en.wikipedia.org/wiki/Basso_continuo

Other references to the term can be found using this search strategy
://www.google.co.uk/search?hl=en&q=%22basso+Continuo+%22&btnG=Search&meta=

I hope this answers your question. If it does not, or the answer is
unclear, then please ask for clarification of this research before
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Thank you
answerfinder

Search strategy
"flute, oboe, violin, viola and" "Bach Quintet in D Major" led me to a
web site which gave the word Continuo. So searched on this word.
?J.C. BACH Quintet in D Major for Flute, Oboe, Violin, Viola and Continuo?
://www.google.co.uk/search?hl=en&q=%22flute%2C+oboe%2C+violin%2C+viola+and+%22+%22Bach+Quintet+in+D+Major%22&btnG=Search&meta=

Quick and correct! It settled an argument.