In Java, the term “Set” refers to an interface provided by the Java Collections Framework. It is a part of the Java Collection hierarchy and represents an unordered collection of unique elements. Unlike lists, sets do not allow duplicate elements.

The Set interface is implemented by several classes in Java, such as HashSet, TreeSet, and LinkedHashSet, each providing different characteristics and performance trade-offs.

Here are some key characteristics of the Set interface in Java:

1. Unique Elements: A Set cannot contain duplicate elements. If you try to add an element that already exists in the set, it will not be added, and the set remains unchanged.
2. Unordered Collection: The elements in a Set do not have a specific order. The iteration order of the elements may vary, and it is not guaranteed to be the same as the insertion order.
3. No Indexing: Unlike lists or arrays, elements in a Set cannot be accessed by an index. Instead, you typically use methods such as contains(), add(), remove(), or iterate over the set to work with the elements.
4. Hashing and Equality: The Set interface relies on the concepts of hashing and equality to determine uniqueness. For an object to be considered unique in a Set, it must have a proper implementation of the hashCode() and equals() methods. These methods are used to compare objects for equality and to efficiently store and retrieve elements in hash-based implementations like HashSet.

Sets are useful in scenarios where you need to maintain a collection of elements without duplicates, or when you need to perform operations such as union, intersection, or difference between two sets.