As in UBS AG:
AG means the same thing as "incorporated" or "inc."

From a German dictionary:
AG [a  ge ]
(pl. -, -s) (f) (abbr) (= Aktiengesellschaft) plc (Brit);corp. (US);inc. (US).


For those interested in more German:
(incorporated company: Comm: Brit, US) Handelsgesellschaft f;
(limited liability company: Comm) Gesellschaft f mit beschr?nkter Haftung;
(Comm) private/public ~, Privatunternehmen nt/staatliches Unternehmen;

If anyone can actually pronounce these words, stop by.

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