It's chocolate-flavored mix for milk; kind of like Nestle Quick but with more health benefits; here's what the website says about it:
The Chocolate Malt drink mix everyone loves!
Chocolatey, malty, and yummy all in one, Ovaltine has a rich, 110-year heritage as a trusted provider of great tasting, good for you flavored milk deliciousness. Ovaltine makes milk work harder by providing a good source of 12 vitamins and minerals in every serving, including 40% of the recommended daily value of Calcium when Ovaltine is mixed with a 8 ounce cup of milk.
Ovaltine delivers great taste with no artificial flavors or artificial sweeteners.
https://www.nestleusa.com/brands/drinks/ovaltine
The malt flavor is great as an ice cream topper too!