What is the distinction between an abstract data type and an implementation of that data type

An abstract data type like a queue supports certain operations. In this case, insert-at-the-end and remove-from-the-front. It can be implemented in different ways using different data structures. One implementation may store elements in an array, while a different implementation may use a linked list.

Similarly, the abstract Dictionary data type, could be implemented using a hash table or a binary search tree.

An implementation is an actual class that you can construct or function that you can call.