Margarine is the generic term for a butter substitute.
The concept of margarine was invented when Louis III of France offered a prize to the inventor of a butter substitute for the poor and enlisted. A French chemist named Hippolyte Mège-Mouriés came up with oleomargarine (the name has since been shortened) and the rest is history.
Margarine is made from hydrogenated vegetable oils such as canola, safflower and corn oil. Although touted as a non-dairy, no-cholestrol alternative to butter, the trans fats found in most margarines due to the hydrogenation process are cause for concern.
To give margarine a more butter-like look and taste, milk, cream, preservatives, food coloring and other additives are frequently used. Regular margarine must contain 80% fat; fat-free margarine contains gelatin, rice starch, lactose, emulsifiers and a lot of water. There are also many butter-margarine blends on the market.