MongoDB is the leading open-source NoSQL database. The most common application of MongoDB is as a primary backend data store owing to its ability to store information in an unstructured format. Besides, MongoDB is considered a highly scalable and powerful database. 

Records in MongoDB are referred to as documents which are data structures with a field and value pairs. MongoDB documents are akin to JSON (JavaScript Object Notation) objects but differ due to the use of a variant called Binary JSON (BSON) that has the ability to accommodate additional types of data. Moreover, the fields in the documents are similar to columns in relational databases. Data types in MongoDB documents can be other documents, arrays or arrays of documents. These flexible documents allow for a change of data-structure from time to time.