Broken means something that is fundamentally flawed and will cause problems: Having good clears and good ganks (
)
Overtuned means they simply are much more powerful than intended because of mostly numbers/items/meta/matchups 
thxs fer understanding
broken -> every new champion or lesser known champion that was played at worlds repeatedly
op -> still 
is just buggy, not overtuned.
Broken champions- 
None of these are quite considered overpowered but their kits have the kind of utility that won't be simply fixed by adjusting or tuning numbers of either their own abilities or items that they build. Attempts to balance them would lead them to being viciously overtuned or ultimately underpowered relative to other champions in similar roles.
Overpowered champs- 
(sorry if you disagree with these it was actually a little hard to come up with a champ that is objectively considered overpowered or overtuned but I feel the community would at least agree with these ones).
Who are you? The nerd lingo police?
I don't agree with the example of broken, but at least you got the general idea right.
A better example would be soon-to-be-changed 
a.k.a. the tanky assassin drain tank with a point'n'click kit.
