In Type Synonyms we read
Just like we can partially apply functions to get new functions, we can partially apply type parameters and get new type constructors from them.
How can a parameter be applied to something else? I think it should actually be
Just like we can partially apply functions to get new functions, we can partially apply type constructor (giving them less type parameters then they expect) and get new type constructors from them.
Do you agree?
The author seems to use apply to mean both "the function to the parameters" as well as "the parameters to the function".
Further down we read
we'll partially apply Either by feeding it only one parameter
Where the meaning is the former, as well as
Let's apply the type parameter to Maybe and see what the kind of that type is.
ghci> :k Maybe Int
where the meaning is the latter.