What is MongoDB and what are its key characteristics?

MongoDB is a popular open-source NoSQL document database that stores schema-flexible BSON (binary extended JSON) documents grouped into collections.

Key characteristics:

• Open source (Community Edition, Server-Side Public License)
• Document-oriented - stores BSON documents
• Collections - groups of related documents
• NoSQL - no structured query language like SQL
• JavaScript interface - interact via MongoDB-specific API

Documents can have flexible schemas - not all documents need the same fields.

Go deeper:

• MongoDB (Wikipedia) — history, architecture and the document-oriented model in one overview.
• BSON specification — what "extended JSON" actually means: a binary serialization adding types like Date and binary data that plain JSON lacks.