"Malt syrup" refers to a thick and sweet liquid that is made from barley grains. It is often used as a sweetener or flavoring in foods and drinks like baked goods, cereal, or beverages. Full definition
I really like rice malt syrup in this recipe because of its more mild sweetness (and I prefer my muesli not to be too sweet - tasting); keep in mind that if you use a different product it will affect the flavour as I find the other liquid sweeteners to impart more sweetness than rice malt. (nourisheveryday.com)