Map Class in Apex:
Map Class Contains methods for the Map collection type.
A Map is a collection of key values pairs where each unique key map to a single value.
Map keys and values can be any data type primitive types, collections, sObjects, users defined types, and built-in Apex Types.
For Example, the following table represents a map of countries and currencies
Country(Key) ‘United States’ ‘Japan’ France’ ‘England’ ‘India’
Currency (Value) ‘Dollar’ Yen’ ‘Euro’ ‘Pound’ ‘Rupee’