less concrete and more accurate definition of a Functor

Co-Authored-By: Jamie Thompson <[email protected]>

Author: aesteve

docs/docs/reference/contextual/typeclasses-new.md

@@ -79,7 +79,7 @@ assert(3 == List(1, 2).combineAll)
 
 ### Functors:
 
-A `Functor` represents the ability for a type containing zero or more elements to be "mapped over", i.e. apply a function to every of its elements.
+A `Functor` for a type provides the ability for its values to be "mapped over", i.e. apply a function that transforms inside a value while remembering its shape. For example, to modify every element of a collection without dropping or adding elements.
 Let's name our "type containing zero or more elements" `F`. It's a type constructor: the type of its values becomes concrete when provided a type argument.
 Therefore we'll write it `F[_]` since we don't really care about the type of the elements it contains.
 The definition of the `Functor` ability would thus be written as: