Hash Map
In plain terms
A key-value structure offering near-constant-time lookups.
Going deeper
A hash map stores key-value pairs, hashing keys to find their slot quickly. It's the same idea as a hash table, exposed as a common collection type.
Under the hood
Performance depends on a good hash function and load factor; collisions are handled by chaining or open addressing. Iteration order varies.
Examples
Java HashMap, Python dict, caching, counting frequencies, indexing.
Think of it like...
Like a labeled drawer system where the label tells you exactly which drawer to open.