Cocoa is a chocolate.
Cocoa is actually a purer form of chocolate and not a lesser form of chocolate.
The cocoa bean or simply cocoa, also called the cacao bean or cacao, is the dried and fully fermented seed of Theobroma cacao, from which cocoa solids and cocoa butter can be extracted.
Chocolate powder is originally from cocoa and is processed with other ingredients; in contrary, Cocoa powder is deemed as the more pure and natural form of chocolate, with no other ingredients added.
Sometimes it's made with nothing but cacao beans, and sometimes it's made with a mix of cacao beans and added cacao butter (that's the fat portion of the cacao bean).
Either version can be sold as 100% dark chocolate because it contains only cacao-based ingredients.
Hot cocoa is usually made from cocoa powder, sugar, and milk.
Because of that, hot cocoa tends to be sweet and light in body.
It often also contains flavoring like vanilla or even spices like ground cinnamon.
So those packets of Swiss Miss you grew up on are most definitely hot cocoa, and not hot chocolate.
Cocoa is by no means a lesser product than chocolate.
On the contrary, it's a purer form of chocolate.
Chocolate has two main components—cocoa solids (where the flavor comes from) and cocoa butter (where the rich texture comes from).
Cocoa powder has very little cocoa butter in it; it's mainly cocoa solids.