Corn syrup is a syrup made from corn.
It is naturally composed mainly of glucose, but usually
modified by enzymes to contain between 42% and 90%
fructose. When used as a sweetener, corn syrup has a taste
that makes it inferior to sugar.
Corn syrup can also affect some people who are highly
allergic to corn. Corn syrup can be less expensive than
sugar though, primarily due to taxes and subsidies. Many
commercial products made in the USA are reformulated to
use corn syrup as production increases.
Corn syrup can be useful in home cooking as well. It is
less likely to crystallize than plain sugar,
leading to usage in frosting and fudge. It is a liquid and
thus does not need to be dissolved.
Cane syrup, golden syrup, and light treacle are
unfortunately not exact substitutes for corn syrup.