More prosaically, it is a sugar made from grains by malting them. The grains might include barley, rice or wheat.
It can come as a thick, sticky clear or amber-coloured syrup sold in tins or tubs, or as a white or off-white crystalline powder with no odour to it.
It is less sweet than honey, and only 1/3 as sweet as white sugar. It dissolves easily in water.
It is used by brewers in making beer. In brewing, only about 60 percent of it will ferment.
It will caramelize at about 350 F (180 C.)
Malt Sugar is also used in Chinese cooking. It can be diluted with water and brushed on the skins of ducks in making Peking Duck.
Use a metal spoon to get the syrup out of the tins or tubs: plastic spoons might break.
The Chinese have made Malt Sugar since at least 200 BC.