As the use of the internet is increasing day to day and so with this amount of data is also getting big. Classical databases i.e. Relational Databases are facing problems during handling huge amount of data as low scalability, real-time data and unstructured data as data on the net is not properly structured, it may be semi-structured or unstructured. So, in order to deal with the problems suffered by the Relational Database Management System, there is a forthcoming category of Database Management Systems that is ”NoSQL”. NoSQL( Not only SQL) databases commonly known as “non-SQL” or “non-relational” databases. It is not the replacement of Relational Databases but it is a substitute for it. In this paper, we will be discussing NoSQL: where they arrive from, why NoSQL, nature of its types and identification with relational databases.