Corn syrup is a syrup, made using cornstarch as a feedstock, and composed mainly of glucose. A series of two enzymatic reactions are used to convert the corn starch to corn syrup. Its major use is in commercially-prepared foods as a thickener and for its moisture-retaining (humectant) properties which keep foods moist and help to maintain freshness. Because of its mild sweetness, corn syrup may be used in conjunction with highly-intense sweeteners.
Corn syrup is used to soften texture, add volume, prohibit crystallization and enhance flavor.
The more general term glucose syrup is often used synonymously with corn syrup, since the former is most commonly made from corn starch. Technically glucose syrup is any liquid starch hydrolysate of mono, di, and higher saccharides and can be made from any sources of starch; wheat, rice and potatoes are the most common sources.
Corn syrup is also available as a retail product. The most popular retail corn syrup product in the United States is Karo Syrup, a fructose/glucose syrup.