Vivendis e aprendendis! (desculpem, não resisti!)

"The value of a Mio euro in US dollars will change with the exchange rate, which was recently about .71 euros per dollar. The prefix Mio is a German abbreviation for Million so at the recent exhange rate there would be about 1.4 Million dollars per 1 Mio Euro. If you have a few Mios lying about - I would be happy to take them off your hands."[ http://wiki.answers.com/Q/One_mio_euro_is_how_much_in_us_dollars]

M: A Nasdaq stock symbol specifying that it is the company's fourth class of preferred shares. Investopedia Says:  Nasdaq-listed securities have four or five characters. If a fifth letter appears, it identifies the issue as other than a single issue of common stock or capital stock.

M: Abbreviation for one thousand. M is used after a slash mark to indicate a per-thousand price or rate. For example, the price of renting a list might be expressed as $50/M names. See also mm.

M = a Roman numeral for 1000
MM: The year 2000 (MM) was a leap year that started on a Saturday

M also means thousand, and has often been used so in various business and other writing.
MM: A million (USA) - the construct mm is often used in technical business writing in North America to mean a million.

Não esquecer:
billion (USA) = a cardinal number followed by 9 zeros (E.g.: 1,000,000,000)
billion (UK) = a cardinal number followed by 12 zeros (E.g.: 1,000,000,000,000)
Source: Answers.com; Investopedia, etc.