A hash, or a hash table, is a data structure that is used to store and retrieve data efficiently. It uses a hash function to calculate the index of an element in an array, called a “bucket,” where the element will be stored. This allows for fast access to the element, as it can be accessed directly using the index.

On the other hand, an array is a data structure that stores a fixed-size sequential collection of elements of the same type. It allows for fast access to elements, but only if you know the index of the element you are looking for. If you need to search for an element in an array, you have to traverse the array sequentially, which can be time-consuming.

In summary, a hash is more efficient for searching and retrieving data, while an array is more efficient for storing and accessing data if you know the index of the element you are looking for.