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What Does Dictionary Mean?

A dictionary, in C#, is a generic data type that stores a set of values with their corresponding keys internally for faster data retrieval. The operation of finding the value associated with a key is called lookup or indexing. Dictionaries are used for faster lookup of stored values. They are intended to be used with any type specified for both the key and value to be stored in the dictionary. They are used to store voluminous data, where the size of the index is too big to hold arrays of the usual data type.


Storage and retrieval are not efficient in arrays when the size of data is huge. This term is also known as associative array, map, table, and in query processing an index or index table.

Techopedia Explains Dictionary

Operations, typically used with a dictionary, are:

  • Insert: Adding a new key and value pair
  • Reassign: Adding a new value to an existing key
  • Remove/Delete: Removing a key and value pair
  • Lookup: Retrieving the value associated with a specific key

A dictionary uses a chaining algorithm internally so that keys that were added last can be retrieved faster in a search of very large instances of the dictionary. A dictionary’s performance can be improved by increasing its capacity to slightly higher than the default level.


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Margaret Rouse
Senior Editor
Margaret Rouse
Senior Editor

Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.