Pronounced "Accidents Grotesque".
History
Akzidenz-Grotesk was released by the Berthold Type Foundry originally under the name "Accidenz-Grotesk" in 1896. Hermann Berthold started his type foundry in Berlin in 1858. The Berthold foundry is famous for creating several new typesetting machines and typefaces, such as Akzidenz-Grotesk (AG). AG was the first san-serif font to be used world wide. As I stated in my Franklin Gothic post, 'Grotesk' or 'Grotesque' was the name used in Europe for what we now call 'san-serif'.
Similarities
AG is commonly mistaken for Helvetica, but AG post-dates Helvetica by 40 years. AG has a more round letterform in its capitals (such as 'C', 'G', 'O', etc.) the its san-serf counterparts. The capital 'Q' has a short ear (leg) offshoot from the bottom-right of the letterform that does not cross into the loop, as it does in Helvetica. AG also has a slab or square dot on its lowercase 'i' and a higher second-story on the lowercase 'a'. Other characters have a more elegant or European-like form, such as the numbers '2' and '7'.
Current Uses
A Chicago company, Berthold Types, ltd. is now the owner of the AG and other original Berthold copyrights. Berthold Types recently (re)released an OpenType version of the AG, named 
Akzidenz-Grotesk Pro, with several world languages supported.
The most popular modern use of AG is in the American Red Cross logo.
Visual Study
Sources
http://www.fonts.com/font/berthold/akzidenz-grotesk
http://en.wikipedia.org/wiki/Berthold_Type_Foundry
http://en.wikipedia.org/wiki/Akzidenz-Grotesk
http://new.myfonts.com/fonts/berthold/akzidenz-grotesk-bq/
http://www.bertholdtypes.com/font/akzidenz-grotesk/proplus/
Images used with permission:
http://3.bp.blogspot.com/-i4Y0KvO6DL4/TbaX0tthYaI/AAAAAAAAIjc/AewNJNTZ-WU/s1600/1873363809_8786cf6859.jpg
http://panhandleares.org/wp-content/uploads/2011/02/American_Red_Cross_Logo.jpg
http://upload.wikimedia.org/wikipedia/commons/d/d2/AGcomparison08.svg
