[getbak]

Originally Posted by Shazam

Malt is an ingredient, typically made from barley but can be made from other grains.

https://en.wikipedia.org/wiki/Malt

More precisely, as it relates to the ice cream: https://en.wikipedia.org/wiki/Malted_milk

Despite its origins as a health food for infants and invalids, malted milk found unexpected markets. Explorers appreciated its lightweight, nonperishable, nourishing qualities, and they took malted milk on treks worldwide. William Horlick became a patron of Antarctic exploration, and Admiral Richard E. Byrd named Horlick Mountains, a mountain range in Antarctica, after him. Back in the US, people began drinking Horlick's new beverage for enjoyment. James Horlick returned to England to import his American-made product and was eventually made a baronet. Malted milk became a standard offering at soda shops, and found greater popularity when mixed with ice cream in a "malt", for which malt shops were named.