Databases : MongoDB is a document-oriented DBMS, with JSON-like objects comprising the data model, rather than RDBMS tables. MongoDB does not support joins nor transactions. However, it features secondary indexes, an expressive query language, atomic writes on a per-document level, and fully-consistent reads. MongoDB uses BSON, a binary object format similar to, but more expressive than JSON.
Schemas : MongoDB uses dynamic schemas. We can create collections without defining the structure, i.e. the fields or the types of their values, of the documents. You can change the structure of documents simply by adding new fields or deleting existing ones. Documents in a collection need unique set of fields.
Tables : MongoDB database stores its data in collections not in tables The collections are the rough equivalent of RDBMS tables. A collection holds one or more documents, which corresponds to a record or a row in a relational database table, and each document has one or more fields, which corresponds to a column in a relational database table.