A dictionary, in computer science, is a data structure that maps keys to values such that given a key its corresponding value can be efficiently retrieved.
A dictionary is commonly implemented as a hash map which allow
O(1) amortized lookup. Alternatively they may be implemented as a sorted list, with lookup requiring a binary search and making the lookup
O(log N) amortized instead.
When tagging a question with dictionary, be sure to tag it with the language being used as well.