What is a Dictionary<TKey, TValue> in C#?

Short answer: A Dictionary<TKey, TValue> is a generic collection in C# that stores data as key-value pairs. It provides fast lookup, addition, and removal of values based on their keys. Keys must be unique Keys must be non-null (for reference types) Values can be null if the type allows it

Example code

Dictionary<string, int> ages = new Dictionary<string, int>(); ages.Add("Alice", 30); ages.Add("Bob", 25); Use case: Storing user profiles by ID, or mapping product names to prices.

Real-world example (ShopNest)

ShopNest caches product prices in a Dictionary<string, decimal> keyed by SKU so checkout can look up a price in O(1) instead of scanning a list.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.