Just the starch from maize i believe. Stuff that will spike your blood sugar levels and make you crash and feel tired when it leaves the blood stream. Better to avoid it as much as possible in your food intake, as it has no nutritional value!
Pretty much exactly what it says on the tin: a syrup which is made from maize (aka corn) starch. It contains varying amounts of maltose (a sugar) depending on the grade of corn syrup, and is also called glucose syrup (although glucose syrup can come from sources other than corn). As it says above, you’re better off avoiding it, as it gives you a blood sugar spike, but your body burns through it quickly so then you have a sugar crash, which is not so much fun.