Set
Noun · Development
Definitions
An unordered collection of unique elements supporting O(1) average-time membership testing, insertion, and deletion, along with mathematical operations like union, intersection, and difference — implemented as a hash set in most languages (Python `set`, Java `HashSet`, JS `Set`).
In plain English: A collection that automatically prevents duplicates and lets you quickly check whether something is in it.
Example: "Throw the user IDs into a set so you can check membership in O(1) instead of scanning the entire list each time."