What is the difference between an ORM and an ODM?
MySQL is an example of a relational database - you would use an ORM to translate between your objects in code and the relational representation of the data.
Examples of ORMs are nHibernate, Entity Framework, Dapper and more...
MongoDB is an example of a document database - you would use an ODM to translate between your objects in code and the document representation of the data (if needed).
Mandango is an example of an ODM for MongoDB.
Essencially, an ORM use a SQL database Driver like ODBC, JDBC or OLEDB to translate the object notation to relational notation and an ODM use a JSON or JSONB api to translate the Object notation to Document notation.
There are different kind of implementations under the hood.
PS: JSONB is a JSON text document notation stored in a binary format as used by MongoDB.