Technically, marshmallows are a confection -- a candy. They've been around in the form we know them since the mid-1800s. A soft, spongy confection made of corn syrup, sugar, egg whites, gelatin, etc. Originally made from a recipe called for sap from the root of the marshmallow plant. (common in marshes). Modern marshmallows contain no mallow plant and was replaced by gelatin, and that is how modern marshmallows are made.

According to Merriam-Webster's Collegiate Dictionary, a marshmallow is:

1: a pink-flowered European perennial herb (Althaea officinalis) of the mallow family; and,

2: a confection made from the root of the marshmallow or from corn syrup, sugar, albumen, and gelatin beaten to a light spongy consistency