What is an MBA?

An MBA is a high-level degree in management . I insist: management. A lot of people think that MBA grads are economists. As a matter of fact, it is very possible to go through a two-year program without taking a single class of economy.
Some programs are specialized (finance, management, international business, etc.). But most programs are generalists with a tradition of excellence in one area (Harvard: General Management, Stanford: Entrepreneurship, Wharton: Finance, Kellogg Marketing MIT Technology).
Consulting firms and investment banks recruiting in general in all programs of the top20.
It is important to note that prestigious programs like Stanford or Wharton offer "dual degrees", in which students can gain dual training in complementary fields. 
Depending on the programs, the duration is a year or two years. A year or 18 months in Europe in programs such as he INSEAD and London Business School. Traditionally, 2 years in the U.S. although some U.S. programs now offer programs in one year (four quarters) . There are also opportunities for "Part Time", "Executive MBAs, distance, etc.
From my perspective, the longer the better, and the value of short-term programs beat me: if the goal is to exchange business cards, a two-day come-to-Jesus seminar should more than suffice. How can one make life-lasting friendships in three weeks?