Database
Database is a physical container for collections. Each database gets its own set of files on the file system. A single MongoDB server typically has multiple databases.
Collection
A grouping of MongoDB documents. A collection is the equivalent of an RDBMS table. A collection exists within a single database. Collections do not enforce a schema.
Document
MongoDB stores data records as BSON documents. BSON is a binary representation of JSON documents, though it contains more data types than JSON.
