In a few words, MongoDB is a database ruled by the document-oriented concept. It is currently the most popular NoSQL database and it is open source. Since 2015, and as of 2019, MongoDB ranks on top of popular databases. 10gen had developed it initially, and it has evolved to be known as MongoDB Inc.
As a document-oriented database, MongoDB stores data in JSON documents with a dynamic schema. So, when the records have to be stored, it can be done irrespective of the data structure. The documents in MongoDB bear resemblance to JSON objects, as shown:
{
"firstName" : "Biharck",
"lastName": "Araujo",
"phone" : "5555555",
"username" : "biharck"
}