An old saying, "The whole is greater than the sum of its parts", expresses the basic meaning of synergy. The word is sometimes used in a purely physical sense, especially when talking about drugs; sometimes a "cocktail" of drugs may be more effective than the sum of the effectiveness of each of the separate drugs. But the word is best known in the world of business. The notion that, when the right two companies merge, they'll produce a profitable synergy seemed exciting in the 1990s, when synergy became a trendy buzzword (even though it's actually been around since the 17th century). The idea of synergy was one factor in what became a "merger mania;" unfortunately, business synergy often turned out to be harder to achieve than to imagine.