Vocabulary - Hash Table

A hash table (or hash map) stores key-value pairs with average $O(1)$ operations:

• Insert: add a key-value pair
• Lookup: get the value for a key
• Delete: remove a key-value pair
• Contains: check if a key exists

A hash set is a simplified version that only stores keys (no values). It answers "is this element present?" in $O(1)$.