A HashSet is a collection in programming that stores unique elements, meaning it does not allow duplicates. It is part of the Java Collections Framework and is implemented using a hash table, which provides fast access to its elements. This makes operations like adding, removing, and checking for the existence of an item very efficient. One of the key features of a HashSet is that it does not maintain the order of its elements. When you iterate over a HashSet, the order may appear random. This characteristic makes it suitable for scenarios where uniqueness is more important than order, such as in data storage or set operations.