Milo is a chocolate milk mix, similar to Nesquik if you're from the US, both made by Nestle. Drinking Chocolate is also a mix, but made by Cadbury, and (IMO) much better than Milo.
Yeah, and you can eat Milo raw or put it on icecream, I wouldn't think to do that with most other hot chocolate powders. Tho I also gather from context that Drinking Chocolate is different?